My JVC PC-11JW will play, but not rewind or fast forward. From what I read, this is usually a problem with the idler wheel wearing out/drying out/becoming hardened. However, when I opened the unit up today and got down to the cassette mechanism, it seemed the PC-11 had a set of gears where the idler wheel is usually located. I did not see a belt or rubber wheel or anything that could really wear out or be replaced. Just wondering what this all could mean, or what I should troubleshoot next.

No not all cassette decks have idler tire, some are gear driven, but look at plastic mounting and it maybe cracked, I see it happen with this model before. 

Yes, I think you're correct. The PC-11JW appears to be gear driven. What 'plastic mounting' are you speaking of, exactly?

Look at one of the levers in the transport when you hit rewind and forward and see if it's wobbling.

Well, the whole gear-driven mechanism where the idler wheel would normally be seems to be loose a bit. It kind of wobbles back and forth in its setting, which doesn't seem exactly right. When I hit RW & FF nothing really happens. It makes a faint noise like it wants to do something, but then stops a moment later.

Are you talking about the levers coming from the RW & FF buttons? Because I don't know that this unit really has any. It seems to be logic controls for all the buttons.

No not the buttons.  I meant in the transport, in the area where the motor is, but sounds like something is gum, or jam up, or it's the the motor itseft is the issue and may have dead spots. would try to turn the gear by hand and see if it hard to turn and take the reel motor out completely apply power to the motor and check torqe, see if it's real easy to stop shaft from turning, it sure take some pressure and if it can startup on it's own from a dead stop. Sometimes, the commutator gets coated with oxides and as the brushes gradually lose contact the coils, then loses power and eventually fails, you have to take apart motor and clean it those contacts, or you can spray contact cleaner into the motor and turn the shaft by hand a few time. If you can take a picture of that area and the motor.   

Yes, I'll take some pictures when I get home tonight. Maybe make a video. Would this unit have a separate motor for the rw/ff buttons from the play button? Because the PC 11 plays fine with no problems. There's just no FF/RW.

Some pics...

Sometimes after fiddling with the various gears, the cassette deck will go into this weird "seizure" mode. That's the only way I can explain it:

Here's a longer video of the "seizure."

http://youtu.be/_uGbQKEZpsk