I notice you didn't say TK50 here :)
I have some TK50's as well. They really are not that bad, the key
problem with them is the bearings in the two capstans: They're old, oil
has dried out, and as a result they drag on the tapes. Plus one of them
has a tachometer wheel under it, and if it doesn't report speed properly
things go bad.
The solution is to remove the capstans and either re-oil both the top
and bottom bearings with watch oil, or replace the bearings with new
ones. I oil them, the modern mobieus watch oils are synthetic and last a
long time. As long as there is no drag you should be good.
One big problem would be aligning them as the height of the capstans is
pretty critical. You can fix this by simply marking the bolts then
counting the exact number of turns it takes to take each one off. Write
it down, and when putting things together put them on the exact same
number of turns. Presto, capstans aligned, drive works for another 15
years or so.
I have a kyroflux I used to image a bunch of Rainbow
Venix disks... love
it, but I've had it a long time...
If there's interest I can image them. If they're already out there then
I just keep em for spares.