i doubt the water is coming in from the gasket, like jim lou said, find where the water is coming in from.

If you want a drain, drill the housing, tap for 1/4 pipe and use a pipe plug. Again like Jimlou said. I do that to all my rears and any 9in i build for our customers.

For the cover gasket, just use silocone, put on a nice heavy bead, cause you have to fill that ring and smoosh the cover on, let it sit overnight and refill the next day.