DEC TK50 common failures?

I'm trying to bring a pdp-11/83 back to working order. Challenge right now is storage - I have RQDX3 and RD54 but the RD54 appears to be unserviceable (never goes ready) and TQK50 with a TK50 which never gets to a stage of allowing me to operate the handle to load a cartridge - the green LED doesn't come on, the red LED is solid for a short time after power applied but then flashes rapidly. I plan to go with an MFM emulator in place of the disk, but would like to get a TK50 working as I have a lot of old stuff I'd like to try reading off cartridges. I have a spare TK50 drive, which behaves exactly the same. The TQK50 LEDs suggest it passes diagnostics, and the boot menu recognises it and will attempt to boot from it before saying there is no such drive. I don't have a spare controller. There is a lot of very detailed documentation for the TQK50/TK50 as far as the electronics and interfacing is concerned but I haven't found much in the way of information about the mechanical side. Are there common failure modes for these drives when they've been stored for a long time? Last time they were powered up is probably close to 20 years ago. Without much in the way of test kit (I have multimeter but no scope) is there anything I might be able to check easily? Thanks, Martin