[Walt Fricke]

Your engine came with the later exhaust valve covers (the 930 part number), with more than the 6 studs the long departed T motor had.

Valve cover stud torque is not critical. The guy who rebuilt my SC motor used a low torque (nuts loosened immediately using a stubby socket wrench). I put a bit more torque on them, but not with a torque wrench. It doesn't leak. I think very few mechanics use a torque wrench for this job - waste of time and effort.

The higher torque you faithfully used can't possibly have distorted anything.

On the older cars with the 6 bolt exhaust cover, when a leak started the tendency was to tighten the nuts more. But that tended to distort the valve cover, making the problem worse.

The much more rigid 930 covers don't distort easily, if at all. But your Rennline covers use an entirely different gasket system than what you took off.

Pull the valve covers and look at what went wrong. If I read you correctly, the leaks are from the joint along the bottom, in the area between a couple of the middle studs, and not around the studs through the nuts? Both sides is concerning, as getting something accidentally wrong on both sides should be less likely than just on one side.

I suspect you will find something out of place or pinched on one of the rubber inserts.