I have a C500-40. it works fine on flat surfaces but when i try to go up an incline it doesnt go, the tires wont spin. I was told it is a clutch problem I just to make sure eveything down from the lever was tight and it all looks good. what shoul i try. I dont want to spend to much money on it because it already leaks radiator fluid into the engine oil so just trying to limp it along.