So it's been cleaned up, which took a lot more work than anticipated. The fan was caked with some kind of mud or sludge, and the preamp module was taken apart and gone through methodically. I almost didn't want to know what went on in the life of the guy who owned it previously...
Anyway it's working, but it's not putting out nearly the power it ought to be. The tech has it back again, and is going through the op amps that get signal from the power supply.
It's got a surprisingly small power amp I'm told, due to the structure of this thing. It seems the 250 through 500 models used the same transformer and big blue caps, but the number of power transistors was the difference in the final product.
But, it sounds like I expected it to, which is great... Hopefully the output comes up to spec, and I'll install it into the sleeve.
Pix to prove it happened!
(Typos fixed!)