The threads should be fine as the "stick" occurs between the bottom of the flange of the bolt (steel) and the cover itself (aluminum.) You are correct, IMO, to only tighten enough to keep it from leaking, no more. A dap of antiseize under the flange is whats called for.
The part that stick's is not "batherd in oil".
The aftermarket bolts with the larger hex's are not so you can tighten it tighter, heavens no. Just so you can get a better grip.