i have some leakage coming down the booster where the master cylinder bolts to the booster in the engine bay... is there a gasket there and does it go bad often? the bolt was a little loose so i gave it about a 1/4 turn to snug it up but i guess it's been doing this for a while cause when i wiped it, it took the black coating off the booster...

anyway. basic question is:

is there a gasket there and should i be concerned that it went out?