MW surVivor ... MT. 279k miles
What is it for, what is the purpose?
i took another look at the diagram and now i see two gaskets! the other one is what you note i reckonYou probably mean the seal. It's there to keep gear oil from leaking into the drum. A lot of diy'ers don't change it much to their later regret.
Just got it off!I use to have an issue on my gen1 tundra where the rear shoes use to seize up sometimes when using the hand brake. You'd notice the hand brake cable hanging loose from under the passenger side rear drum to center of the differential. Those external hand brake drum levers for the cable would seize up at their pivot points. You'd need to take them apart, clean, and grease them good. At times when i found them struck, i carried a 4lb hammer, and gave them a good whack to free the brakes until able to fix the issue.