I keep having issues with leaky coolant o rings on my 07 YZ450F- the ones that seal the solid coolant pipes near the exhaust header and the water pump. It's worst where the coolant pipe fits into the head near the exhaust header. I use Evans/Zip Ty coolant and it seems to deteriorate the o rings so they get hard and leak. I do mostly woods riding and with the rekluse clutch the evans is the only solution that keeps it from constantly boiling. It's either the coolant or the heat, as the evans coolant allows the engine to run a bit hotter (doesn't boil, though!). I was going to get some viton o rings but I don't know the exact size to order. Anybody have any advice?