Good morning, Sir. And welcome aboard.
I also have a 101.27440, acquired in "reasonable" shape. The only problem I ran into was also with the threading change gears in the QCGB. I don't want to appear as the end all, know all, expert on this machine. But on mine, the change gears were not steel, they were "Zamak".
Be sure to remember
never to use a chlorinated solvent on zamak, it will turn into powder in short order. Zamak is an aluminium and zink alloy, with some other stuff thrown in in small quantities. It decomposes aluminium, leaving the zink as a granular metal residue. I use a carburator cleaner based on isopropyl. (rubbing alcohol) I figure if it won't melt a carburator, it won't hurt my machines.
Steel, brass, aluminium, zamak, and plastic (printed) gears will work. Their density would determine how long they will work without wearing out. When I started rebuilding mine, I didn't have access to any experts. But I waited patiently and watched things on the sales sites and eventually found a few replacement gears. Zamak... ... I'm old school, I don't trust plastics. And really wanted to stay OEM if I could. I have been told that for threading, plastic gears will last a long time, but I'll stick with OEM.
The gears will be 16DP, with 14-1/2 pressure angle, 3/8 wide. The most likely failure is in the 30 tooth gears. I bought a couple of extras, they're still tied (baling wire) to the back of the machine. Hope they stay there a while... ...
My opinion of "experts" is a little lower than a used car salesman. And, as an engineer I am often referred to as one of them. Ces't la vie... ...
Bill Hudson