I have to second what Doug and Frank said. If the machine is set up
right and doesn't have any nasty problems (such as the issues with
the machines we've seen at the Mellotron Ranch), you won't be
spending a lot of time on maintenance.
Keep a flat blade screwdriver and nut driver handy to adjust a key
once in a while, and that's about it for anything semi-regular. You
may want to maintain the tape path by cleaning it up a bit and
demagging the heads, same as you'd do with a tape deck, but this is
every once in a long while and not a constant demand. Now and then
check out and oil the motor. Else these things require little
maintenance, provided they're good/stable to begin with (and there
are several people on the list who can help set a machine right if
it's in rough shape).
If you're moving the machine around a lot, using a variety of tape
stock, experiencing humidity/temperature changes, and so forth, yes,
you'll probably do some additional adjusting of the pressure pads and
pinch rollers to compensate for this.
But it's not like these things blow up all the time or fail
miserably. They're probably just like anything else for reliability.
See what Duncan has to say about this topic:
http://www.kleonard.com/music/concerts/rmi040508.htm...kl...
M400 #805 - knock on wood
M400 #1037 - reliable...? tell that to my first motor...