Hey Jon... replacing caps, transistors, and checking resistor values is pretty simple and something nearly any amp tech could do, though finding the transistors can be tricky. I did mine myself. For the most part the larger exposed cap cans can be rebuilt, but they are pretty sturdy compared to the others inside.
I spent about three hours reading every repair thread on macs here (a couple of great videos btw) and I spent about 90 minutes searching and tracking down code equivalents and sources for the transistors. I ended up ordering from mouser, as other suppliers are apparently in the biz of counter fitting them. Some of the hifi forums have a lot of information on these.
Most of the schematics are available online.
For rock solid diagnostics or to repair a non-working unit, (I think) you'd be best off finding an experienced mac guy.