Oil leak

My '50 Ford has a fresh SBC in it. It has developed an oil leak that causes the oil to drip from the bellhousing (it's a 4 speed). The guy who machined the block said 90% of the time it's from the pan becoming loose and even if it's tightened, the oil will find the path. The clutch has started slipping as a result. So, how do I tell with the engine not running if it's the pan gasket or the rear main seal?

 

is the back of the pan clean?
just oil on the bell housing?
if so chances are ..its the rear seal

 

if it’s coming from the outside of the bell housing and it isn’t gear oil, its prob the oil sender or compression fitting (if you have a mechanical gauge. It could also be the back edge of the intake where it meets the block
If it’s coming from the inside of the bell housing and it’s not gear oil, its prob the rear main seal or the back side of the oil pan gasket isn’t seated right

 

Often leaks that LOOK to be coming from the rear seal area are a result of a leak at the back of the intake, especially when the builder/***embler insist on useing the gasket across the rear of the manifold.

Yea, I know all about it...

The oil can leak into the bell housing where it meets with the block...

 

if you have the luck i have..it will definetly be the rear main seal..and when you finally get at it and go to repair it..you will figure you will not need the input shaft seal for your trans, and not put it in..and after you get it back together..that will be where your next leak will come from

 

You can count on three things with a SBC: they will be reliable, the parts will be easy to get when you need them and they will leak oil.