Moped Army

ok here's the deal

i just bought a 1980 puch newport II like two weeks ago maybe.. took it out for a test ride and it's working great. after about a half hour of good solid flat out running it just loses power and craps out.. won't start again. i have it on authority that "there is probably something wrong with the transmission"

ok

so can anyone give me a run-down of some of the common failure points of the puch za50? what should i look for? i drained the ATF and opened up the transmission casing; most of the transmission fluid was red, but the dregs are gray, like it is full of metal powder? feels a little gritty.... but, you know, nothing like fell out of the transmission when i opened it, and all the gears that i can see look okay, nothing shaved down or no missing gear teeth, stuff like that..

also, i want to try and take the transmission apart further, but i have to "lock the drive gear hub" blah blah blah and of course this requires a special tool according to the service manual. does anyone have a good home-brew method for locking this shaft up so i can remove the gearing from the transmission? i'm thinking that maybe once i can get deeper into it, it will become apparent what's wrong.

and, i guess failing all this

how eassy is it to just stick a one-speed on this thing?

thanks in advance for any help