They are infinite in the reverse direction, but the forward direction is a little high. I've ordered new diodes and a replacement for the transistor. We'll find out in a few days if that was it!
The diodes wouldn't cause the higher output voltage. The drop (forward voltage) across a silicon diode depends on the current through it. Look up the data sheet for the diodes you have and check the specs. I've seen a few different failure modes for rectifier diodes, basically shorted, open or leaking, and they're not subtle like too high a voltage drop. For the cost you can shotgun them easily enough but I'd be doing careful measurements and compare to the schematic to see where the real problem is.
Mark K5LXP
Albuquerque, NM