Many times ive had old drives, or ones that have sat unused for long
times, not spin up because of the spindle bearing lubricant either draining
to one end of the bearing or drying out entirely. I've seen this in quantum
drives a _lot_ and have also rescued a couple maxtor ESDI drives this
way- i open the drive up in a nice dust-free room, take off the spindle cap,
and put a good dose of zep 45 on the bearing. LEt it sit overnight to
soak through, (after reassembling the drive housing and so on, of course,
you dont want it to let a nights worth of dust and dirt in!) and they spin up 
like a champ.  Something ive noticed in some of DEC's older drives (an RZ58
isnt _that_ old! ) is that the rubber stop guard to keep the head assembly from
hitting the housing gets old and jelled, and then the head arm sticks to
the stopper. Ive done this on an RD53 once, just open it up and put
a tiny piece of thick paper over the stopper (the gummy rubber will stick
very well to it and hold it there forever)  and clean any gummy stuff off the
arm. Then the arm can move and the drive will spin properly. (otherwise its askin g
for a head crash)   Smacking the drive will get it going if the bearing is
not properly lubed, but a better solution is to relubricate it. 

YMMV

happy hacking,
isildur