Eddie, I doubt you'll ever need to change one, as much as I've tortured them the past 4 yrs I've never had one fail. The motor I just changed in my 850 is a 942D (I think) with a 516:1 head.
Frank had those mini brushless motors custom made to fit the narrower axles on his B4206 & WA500 loader. The brushed motors are too long. My other B4206 with hyds, they have brushless motors in them that I had to file down the "bells" to get them to fit, there's literally 1mm between the two of them, they run a lil faster & a lil more powerful too, bigger diameter bell.
I hope you can find time some day again soon Eddie to get back at 'er with your hobbies... and prod your neighbor Ayoub while you're at it, he's been dormant a long time too.
Evan, these conveyors came from
https://rcmodeldesign.com/ I saw them listed in the description of RC Sparks Youtube Gold vids. There a lil over priced for what you get... the vulcanizing on the belt splice was near perfect, can barely tell where it is, that's about all the positive I can say about it... if I do buy any more conveyors it will be the TeleTracs from Model Tech Winter in Germany, I'm sure you've seen his vids on utube & facebook.