Well I got the SL-5600 working. Before lubing the capstan/threading motor I didn't find any voltage on its 2 top terminals (the bottom connector is too hard to get a meter on). After lubing the motor I couldn't figure out how to make it work on the bench, resistance were 200 ohm at lowest so I figured it was shot. I reassembled the mech and decided to try a tape...to my disbelief it threaded it and then played it back just fine.
Tuner won't pass decent video from the antenna (snowy negative without color) but it tunes sound fine. I'm probably going to leave the tuner alone for now since it doesn't really NEEED a tuner. Tape playback is enough to make me happy.