I should revise my post about possible leaking seals etc... after the synthetic swap. I have been doing a lot of reading on this, and it seems to be a myth. If your engine has a leak now, it will have a leak with synthetic. The base stocks used in earlier synthetic oils were incompatible with conventional oils and actually caused seal damage. However they are now compatible as stated in the amsoil website as well as the mobile website. It seems that conventional oils would damage engine seals, and synthetic actually can recondition them over time. If the engine leaks, its possible for the syn oil to soften the gasket or seal enough for it to stop leaking. I will put this theory to the test with my recently aquired 175,000 mile 22r-e with zero leaks currently using Valvoline durablend. I will be doing the amsoil engine flush, and then using amsoil 10w-30 and the super duty amsoil oil filter.   wish me luck!