I guess you are right about that. Sorry there is no good manual out there.
Europeantransmissions has one but I guess it's like ATSG. Tried to order one it's say the manual is a download but when I tried to order they charge for shipping and expensive too shipping would be to Europe but I did not order. They did not answer my mail I usually don't order from such company.

Update on the project: On Monday I will take apart the extension housing and I have spot some burned steel discs. tried to find a place where I can buy steel disc but I did not find a place where I can see the price on them.