I just had a gear change done a few weeks ago and the mechanic that set it up used a gasket. If you do a search on biggearhead I think you will find that not many know more than he does about rear ends. ( the type in cars anyway)
I would go with what he says. Don't mean to make his head swell up but he was a wealth of information and very helpful with me.
Last time/first time I had the cover off mine, I installed it with gasket and permatex #2. It don't leak, but I'm sure there will be some scraping to do to clean up the surfaces when it comes off again in future. If I was doing it now I'd use permatex on the cover with a gasket and a thin continuous bead of RTV on the housing and install it not too tight and tighten the rest of the way after the RTV cures.
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