My only experience in this area was when I was bolting things back together after removing the head and replacing the turbo on my 82 GLT.

Someone here suggested using a high grade silicone in conjunction with the new O ring on the turbo pipe/block connection. It worked like a charm. The wet silicone acts like a lube and allows the O ring to move freely so it doesn't bind when inserting the pipe into the block. I cleaned all the surfaces with lacquer thinner prior to assembly to insure good adhesion. It has not seeped at all since assembly (1 year/11,000 miles).

I use the same procedure when installing the O ring between the heater pipe and waterpump (adding a modest coating of silicone to the rubber seal between the waterpump and the head as well) It has contributed to a good track record in that area as well.

Randy