If it won't turn by hand, don't jump to the conclusion that the bearings are seized and you need a new alternator, here's why:-
I was having bother with mine seizing up while I was away at work for 3 weeks, when I came home I would have to
"persuade" it to turn with a pipe wrench, once I turned it a couple of times it would free up and would be fine while I was using the car daily, then when I was away for 3 weeks it would seize up again.
I assumed it was the bearings, so after a couple of months I picked up a couple of bearings and removed the alternator to replace them.
To my surprise
when I removed the end caps the bearings were fine
( they are also pretty substantial and good quality)
On closer examination I discovered the problem.
It was a build up of rust on the field coil formers
(the laminated metal part the coils are wound round) and on the rotor.
The gap between the rotor and coils is only a few thou so it doesn't take much to close it, that coupled with the
(relatively) large surface area involved is enough to lock the alternator up.
I cleaned up both surfaces with some fine emery cloth
( taking care not to damage the insulation on the field windings) and gave them both a very thin smear of grease.
I rebuilt the alternator with the original bearings and put it back on my car, it's fine fine for the last 6 months
Having seen the quality of the bearings and the clearances of the rotor and taking into account the position of the alternator on the car, under the engine vent.
I am pretty sure that this is root cause of many of the
"siezed" MK1 alternators that we hear of, if that suspicion is
correct then the repair is both cheap and relatively easy
HTH
Jimi
