I've got a friend that built a 383 with a vortec engine. He says under high rpm the plastic timing cover leaks around the mounting bolts. He has replaced the cover twice. Last time he drove it at around 2500 and rechecked, no leaks. Took it out the second time at 7000 and with a black light could see it
leaking around the timing cover bolts. Any suggestions?

 

I'd be double checking that the block surface is spotless and true, and if so, may be concerned about excessive oil pressure?