Nitrohead I understand what your saying about the wait and see thing on the Manic's belt durability for offroad use. Thats why I wont say for certain dirt, little rocks, sand or etc wont effect the Manic's belt drivetrain until I fully test one out. I'm as curious as you are about it.
Now the Sx belt/idler,spur doesn't seem to have a issue with dirt clogging things up. Though the drivetrain is centered in the middle of the chassis were as the Manic is on the right side. Will wheel spinning when turning your front wheels push dirt up in there to cause a problem being open like that ?

I do have to hand to Schumacher though for putting a belt drivetrain in a 1/8th scale. All my Nitro 1/8th scale 4wd Rc's are shaft drive..

Below - Elven is working on a shaft driven Warhead



Elven Wizard