Vintage Synth Repair

I'm trying to make some sense of these nice little synths. Info is a 
bit scarce though.


It appears that there were four versions of the Arp Prosoloist.

The Soloist. Earliest. Never seen one.

The Model 2710 Prosoloist. The Genesis machine, with the 4034 "Moog" filter.

"Early" ProDGX. Model 2720. Push-button patch selectors. More robust 
cabinet. Button graphics had various colors. Orange, green, etc. 4034 filter.

"Later" Pr0DGX. Model 2731. Same layout as early ProDGX, but all 
orange letters. 4075 filter.


I'm wondering if anyone can confirm this info. Specifically, when did 
Arp change from the 4034 filter to the 4075 filter? Are all Model 
2720's 4034 filtered?  Were all 4034's potted? Or did Arp stop 
potting them for the Model 2720?


Thanks!

Jim Blair
Ape Island Sound
Nanaimo BC
Canada