it "restores" the elasticity to rubber type oil seals (swells them), Not certain if it changes viton products (wouldn't think so). I can't see how it would cure leaks from the gaskets that are fitted to our 4s except for the rocker cover seal. It was meant for "curing" leaks from crankshaft oil seals etc on cars. Our local stockist says it works great for that but I wouldn't try it in our engine/gearbox combinations especially with the wet clutch
Now here's a thought; I wonder if it would work on my intake manifold rubbers if I soaked them in it?
Rob