A couple of years ago, I was traveling with my F-53 Chassis, class A Motor Home when I notice the smell of gear oil. Checked the rear axle and the inside of both inner rear rims were covered in gear ...
Just plugging the vent shouldn't destroy the seals. They will leak from the pressure but if caught soon enough, they will seal back up as soon as the internal pressure is taken care of. Of course you still have to deal with any damage done to the braking material from gear oil.