New subscriber here. I have a TC-K65 and it has a similar problem: not engaging the pendulum gear in FF/REW. It has a friction clutch underneath the gear and the friction from that is supposed to rotate the pendulum arm. The friction is adjustable by putting the plate spring on different height steps. No matter what I tried, it does not want to work, it engages slowly in one direction, and not at all in the other direction. Mine behaves much worse than this one. The felt disc might be worn out in mine. The arm is moving freely enough by feel, so it's probably not a stickiness issue. I'm looking forward what problem will you find with yours. I've only done some preliminary examination on mine. It still has all original belts.
Might be worth me doing a full service video on this unit, then when I can get back to it. My first suspect would be glue or some other gunk on the felt causing it to not slip as well anymore, followed by the felt itself degrading.
I think no, the problem is not that it's not slipping well enough, it's the opposite, it's too slippery, so it can not transfer enough torque towards the pendulum arm to rotate it. The felt disc seems unusually thin, maybe it got ironed flat and smooth by the 40+ years of constant tension. Glad that the magnetic clutch is seemingly still fine in mine, I had no idea about the playback takeup clutch being magnetic. @@Oklawolf
The transport has to be unscrewed and moved back to get at the lamp. It's a T-3 (3mm) 6V lamp. I have newer videos on this deck you can watch where I go through servicing it, but if you're just replacing the lamp I think it can be done without doing much disassembly. Just remove the cassette door, take out the four screws holding the transport, and work it backwards until you can get to the lamp.