Originally Posted by David1971
When added to the crankcase, will Marvel cause seals to leak in a high mileage engine that has previously not leaked? I have always been told never to switch from conventional oil to synthetic for that reason.

Sorry to stray off topic a bit, but has anyone had experience with Rislone Engine Treatment? Is it more aggressive than Marvel?

Thanks,
David

I think Rislone is essentially kerosene. I have also poured kerosene in an engine after draining the oil and putting the plug back, then let it dissolve the sludge.
But in my 413 I had dropped the pan and cleaned it anyway.