As far as I know the oil leaks in the 117 alloy engines head gaskets are limited to just leaking oil. Your 450 is not an alloy engine, it is an iron engine. I'm not sure if these tend to progress into the water jackets or cylinder. Therefore I belive you can drive forever with either an oil leak from the head or rear main seal, providing you dont run low on oil.

On my 560SL the oil would leak out of the head and fill the valley between the two cylinder banks. It would then over flow out of the back and dribble through the crank shaft sensor port and come down at the bottom of the bell housing just like a rear main seal leak would apear. You can search on some of my earlier post of about February March 2005.

As far a a 300 six I have no experiance with a leaking head gasket.

John Roncallo