I found this today while going through some paperwork from the old Moog Music service dept.
I have some of their original factory folders.
Many interesting mods, cures and production changes are described for what are now vintage Moogs.
I’ve uploaded one below that recently had its 25th birthday.
It describes a retrofit spring-return mechanism for Moogs with modulation wheels.
Fascinating find, Kevin! 
Have any other interesting things in that folder collection? I love the bottom of the page with all the Norlin brands. Nice history! 
I did not know that Cordovox was a Norlin product. I played one once, what a cool machine. (for a ‘cordeen’!)
This really dates me, but a guy I gigged with for a few years had a Cordovox accordion with a Leslie 860–a reasonable B3 sound without the weight. 
Sure looked weird, though…