more then a 100k on a 2 stroke!!!! that's amazing!! Polaris out to put it in a museum. Has to be the highest mileage atv of any kind ive ever seen let alone a 2 stroke! Sure that's not 13000 not a 130000?? Keep in mind if you replace it to get the power level of your 400 2 stroke your going to have to step up to at least a 500cc 4 stroke. even then down the fireroad id bet your 400 would leave a 500 four stroke. But the 4 stroke will haul more and have more torque. Opinions aren't worth much but ive done the Polaris's Ive done the Hondas and ive done the yamahas. If I were you id look real hard at a 500 Yamaha grizzly. Bullet proof machine. My 700 hasn't cost me one penny other then gas, oil change and one plug at 4500 miles. Forgot at 2k I put some better tires on it. I have NEVER once heard of even ONE grizzly owner that had a problem machine. there may be faster 500s and 700s and maybe Polaris rides a bit better. But NOTHING is more reliable.