it had the tires on it when i got it and does not seem to have been mud riding at all the guy i got it from had it on a farm.one of the axles in the front the boot on the inside is twisted up a little so i know i have something to address there.i did look at it in the mud and i dont think it was spinning thats what has me concerned but like you said it could be a spline stripped or something.i just got this thing friday and i am just wanting to fix any problems it has.i just dont know the way the 4wheel drive works or if it is just not the power there to always spin the tires.i stuck it on a hill were the backend was bottomed out and the back tires were spinning but the front were not