Mike, I've spoken to two different repairmen about my own MX, both indicated that parts were becoming hard to obtain and that the MX's are prone to develop electrical problems.
However the usual problem is with the o/off meter switch activated by the film advance, and I was told this was a simple repair. Usual signs are complete electrical failure, including the hotshoe/x-synch.
Unfortunately the minimum cost of repairs now is often more than the price of a mint model on the auction site, so its difficult to make a decision.
Ian