1.) MD6 stuck to "1" was a shorted diode on the bus load board. Changed to a "D664" to a 1n4148 (the best I got home). 1N3606 is listed as replacement, what other diodes can be used? 1N4148 seams to work in some way.
I actually measured it before I solder it onto the board. I'm not 100% sure that is was a 1N4148. I measured the forward drop to 0,60V, the ones that's mounted on the board measured to 0,58V.
Interesting read, good work as always Anders. I might try this myself sometime in the future, so it's a good reference.
Markings "Q2132" or maybe with a leading "O" och "0" doesn't give anything. "7629" is the date code.