I use Permatex #2 for that sort of stuff, as truckernix said "the brown gooy stuff that doesn't seem to harden"

Not as a gasket replacement but as a helper for the stock paper gasket.

Also be sure your surfaces are flat, and that the bolts are not bottoming out in the holes.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-