I know, another thread about fluid filled rears but this one is a little different. Went to check air pressure yesterday, yes the valve stem was at 12 o'clock, but had not jacked tractor up (didn't know about that until reading it here). Anyways, what appeared to be oil came out of the valve stem. I would have expected water, but this was brown, thicker than water, and slippery. Are tires filled with a petroleum based product to prevent freezing and corrosion? Any clues would be appreciated.