The booster I ordered from Rockauto did not come with a new mounting gasket, so I had to order one from Mike's Montes. Its not a part most places bother to carry. The old 9 in dual booster in my Regal lacks the vacuum port.
I assume you mean the gasket between the booster and the firewall? Did your RockAuto booster come with the "plunger" from the booster to the Master Cylinder?
Yesterday I picked up my Master Cylinder for a 1990 Caprice:https://shop.advanceautoparts.com/p...-10-1870/5352363-P?searchTerm=master+cyl
Was only $25. Even if the master Cylinder ISN'T leaking causing the paint on the current booster to come off, having a master cylinder that sends the PROPER amount of brake fluid to the upgraded rear discs CAN'T be a bad thing. I'm excited to see what all I've been missing all these years with my back brakes!
My Booster should be in today. Which will give me a matched booster and Master Cylinder. (for a 1990 Caprice) I can get it all installed over the weekend.