Ya, i hate that. Diff cover bolts. Yet all i ever use is ultra grey or ultra black. But i dont pound it on,and i let it sit for 10 minutes before i assemble. Its like people fill the bolt holes first. I go around them. And every single fwd car i do trans service on.
I bet you do a nice job. I've seen RTV in some shop manuals. Like you describe - instead of a gasket - not gooped on to try to 'improve' the sealing.
I still mostly prefer just a plain rubber gasket for ease of removal and prep for a new one.