I have had my 857D since new and it has taken a lot of abuse while in etc. Eventually, my selector knob became *very* loose, however it kept working, though I have noticed the skip thing from time to time, sometimes even going backwards!
I inspected the board and came to the conclusion it isn't very user-replaceable, but then I haven't done repairs of that kind in years.. umm... decades now. However, if someone can point out the replacement part, I'd appreciate it, as when I was moving the radio from the house to Jeep tonight, the darn thing came out, shaft, knobs and all and I haven't even been able to locate the missing shaft and knobs (yet)... it's still dark out, but the snow may not help either. Thank goodness for the fancy microphone, which can do partial duty in the meantime.
The local shop said that attempting a repair may be close to as much as a new radio, but I don't need nor want a spare 857 "body" due to needing a replacement "head".
Modified Dec 29, 2011: I found a service manual online and while the board the encoder sits on is not a replacement part, there is a part number provided for the encoder in the parts list along with the OEM part. The part specified is no longer in production or available from 3'rd party, however Yaesu is still making the radio, so there is likely an upgraded or equivalent part number. I've asked one vendor in email about that possibility. I may have been wrong on my initial assessment, as I may not have disassembled the head far enough to truly see where the encoder was mounted.
Modified Jan 4, 2012: I disassembled the head last night and it looks like an easy repair if I can get the encoder. I haven't heard back from the parts supplier yet, so I dropped Yaesu / Vertex Standard a line themselves.
It seems the shaft is perforated from what I can see and that the hole in the head it goes through isn't tight enough to provide support, so if the shaft gets lateral pressure, it can easily snap off the small sections where the shaft is perforated, especially with the leverage provided by the length of shaft.
Modified Jan 12, 2012: Yaesu / Vertex Standard has the parts in stock, so I'm going to order a couple. While I'm at it, I may try to "engineer" some way to fill the excess space in the faceplate around the shaft to stabilize it and reduce the chances of it having lateral loads applied to break the shaft. I obviously don't want to get it too tight so it is tough to turn either