I have ordered boatanchor radio parts for my Nationals from Gary and have been happy with both the purchase experience and part performance.

 There are service bulletins that made the SB-102 a better xceiver:

 http://www.nostalgickitscentral.com/heath/Service_Bulletins/sb102.txt

 More restoration information and personal conclusions about the SB-102 here:
 
 http://www.nostalgickitscentral.com/heath/heathkit.html

 It may be easiest with the chassis out of the cabinet and the meter removed. Handle with care. Anything to give you more room.
 A small automotive seal pick with a hooked end is also a useful tool as the needlenose requires you to pinch the string to hold it.

 A couple of friends and myself plan to be there early Saturday. It may be a better venue than the Monroe Co. Fairgrounds and Barnard Fire dept. field have been.
 Hope it doesn't rain (too much). We'll see.

 The National Archives on QTH.net is still active for National help.
 As for appearance restoration, I find that auto body shop supply stores have many products for cleaning, polishing and appearance care.
 The Hammered finish gray paints can be a close match for the Nationals. The Textured satin black or gray isn't really a wrinkle finish, but if the whole cabinet needs paint and you aren't a stickler for authentic restorations it looks good for little cost.
 A set of small stiff brass and nylon brushes for cleaning helps. They can be made stiffer by shortening the bristles. Cotton rags and not paper towels. If you use steel wool, blow the work off with compressed air when done. You can take decades off an old unit. Do one section at a time.

 That is an interesting transceiver. Looking at the front panel, I would have never known that it housed a CB (11/10m) transmitter. Is your clock and dials backlit white?
 I have been a Hammarlund fan for decades.

 If it is not oscillating but has a harsh tonal quality, make sure that the power supply filter caps are 40 mF. I used what I had on hand (68 mF-more is better?) and the set did not like this. Besides the slight delay in powering down after shutoff, it brought the B+ up and the audio quality suffered. After installing the correct values, the set sounded good.
 On your 183D, C-65 off the B- line should be installed 'backwards' (plus side to chassis)as the chassis is more positive than B-.
 There are some excellent threads in the National Archives on the QTH.net website that address fixes for issues that others have found:
http://mailman.qth.net/

 I am baffled with a National NC-98 of mine with the similar rf or if overloading problem. Bringing up the RF gain control on AM in AVC mode, the S-meter will nearly peg with or without an antenna attached and has a severe audible or inaudible oscillation. The AVC voltage goes to minus 16 volts during this oscillation.
 If I reduce the rf gain, flip to standby and back to receive, the receiver will return to a somewhat normal state of operation and the S-meter will work normally. Like a tube was blocking.
 Before I recapped the paper/foil caps and reresistored it, it behaved with much more stability. The 100K screen dropping resistors were at 24 meg before replacement.
 If I detune the if transformers slightly it will work almost normally, but with less sensitivity and poor tone.
 This National doesn't have the selectoject filter, but does have a crystal selectivity circuit before the 1st if. Even with that function off, it still does this.
 Note: the 2nd if transformer did have a frozen slug and the cardboard winding tube was damaged slightly in replacing the slug. Could this be the culprit?

 May 5th.
http://www.antiquewireless.org

 I have the NRD-515 with the matching memory unit and speaker. The previous owner installed the optional bandwidth filter, headphone jack and memory back up battery pack. This robust radio is built like a brick and is as close to 'boatanchor' as a Japanese radio could get. I just love the feel and capability of this receiver.
 The later NRD/NSD series units may have had more bells and whistles, but the 515 is a legend. They hold their value well as the asking prices are quite high.
 I have been on the JRC archives website hosted by qth.net, but it has been quiet lately. Maybe someone there has scanned a service manual?

 Another brand name was E.F. Cannon of Springwater, N.Y.

 I find that a 50' or 100' spool of 16ga stranded random long-wire works for my purposes. Most auto parts stores sell a spool of this wire for cheap. I have the room for an inverted-L across the roof (E-W) and down the side of the house or a (N-S) sloper from the house roof to the garage roof. Both give good omni-directional reception.
 As mentioned previously a good ground may cut noise and increase gain particularly on lower frequencies, except if this is an AC-DC boatanchor (don't ground this chassis).
 Lightning protection is important to protect house and property and maybe equipment unless your antenna is run inside across the attic.
 A quality receiver with a good RF amplifier and preselector section can make DX listening much more enjoyable than a mediocre receiver. 

 I have the R-390A, which is a different radio in many respects but I have taken it apart and put it back together again. It is a very mechanical radio compared to what we have today. Grand machines!
 First you'll need the technical manuals for study and reference when servicing anything. Online resources, especially those who have serviced these are indispensable.
 By rocking the MC change between 7-8 or 15-16, is there then any response on the 8-15 mc bands? The tech manual gives test points to use at a tube socket terminal to check resistance to ground. This could help verify an open bandswitch leg.
 Check the test point voltages and AGC voltages to see what drops out and where it comes from between when the radio is operating and when it dies.

 PS- Another thought would be that if operation is restored after grounding the antenna, maybe a tube voltage is drifting up and 'blocking' the tube?

 It probably isn't a tube. You have a schematic to go by, correct?
 Many times I have gone through the assembly manual and placed another check mark next to the assembly step check mark to double-check the integrity and placement of that component.
 I would think that a possible leaky cap may be pulling the line down. Follow the line on the schematic with a high-lighter marker and lift suspect component leads until the voltage comes up. A warm wire or component may be the culprit, or be on the path leading to it. Is the draw lifted in standby? Use safe handling  pre-cautions and practices around high voltages.

 Ditto on the dominos. I have some early FM radios that use them in parallel with a resistor in the RF sections. You can't tell if they are leaky until you lift one side of the resistor.
 Cheap (esp. grainy finish) resistors can drift very high. I just did some 100Ks that measured 24 meg.
 Mouse piss can corrode and open choke windings. Beware cleaning variable air and mica caps with solvents, as that can drift them to another frequency threshold far from spec.
 Spread and/or dirty tube pins/socket terminals can be noisy or intermittant.