What am I doing wrong? I rebuilt the 350 in my 69 three years ago. Had a machine shop go through it and it runs great but it continues to leak at the front seal. I've replaced the front seal three times, balancer twice including going to the larger one, and the timing cover once over the last three years and it's leaking again. Each time it doesn't leak for the first few months. This is not my first motor but the last one I did was some 30 years ago. I'm stumped. Any ideas would be appreciated.

 

Every one of the late model vortec blocks that I take apart has a dab of silicone in the key way. Might be where your leaking is coming from

 

Or a distributor gasket between the crankshaft sprocket and dampener.
Old school.