rear housing ???'s 87 r10 swb 10 bolt

[LONGHAIR]

That "over flow tube" is really a vent. It should have a plastic "cap" at the top. That is a check valve that is supposed to let air pressure out but not let water in. It should be connected to a metal fitting. Many times that fitting is also the bolt that holds the "junction block" at the end of the rubber brake line. It screws into the axle tube, connecting the rubber line to the housing and serving as the mount for the metal lines. IIRC, they are usually brass, so there shouldn't be a rust issue.

As far as "adding lube", there should be a plug on the side of the casting on the front side of the housing. It is up near the pinion above center. It should have a square recess. You just insert the drive end of a 3/8" extension into it to remove it. It has tapered "pipe" threads. You fill it to the bottom of the threads....meaning that when it runs back out at you, it's full.