They tended to leak even when new. If you have lubricated the knuckles with
140W oil as most sources recommend, some leakage is inevitable. They will leak
past the bearing seals into the bearings under hot, heavy use, and from there
out the bearing cap onto the tire. They will leak past the knuckle seals. And
they will leak past the bearing caps as is happening in your case. I use 140W
oil myself and have to check the level in the knuckles every time I drive the
jeep.
>There was even one "mechanic" who recommended draining the oil out and
> replacing it with bearing grease.
This is done commonly and has been recommended to me by people who have worked
on hundreds of jeeps. Some maintenance manuals even call for chasiss grease as
the proper lubricant. I used it in a jeep I have since sold because it leaked
so badly. I guess you have to trade off the improved lubrication of gear oil
against the greater chance of running the knuckles dry inadvertantly due to
leakage. It may also depend on the type of U-joint, cardan cross, Rzeppa,
whatever, since the CV type joints have more sliding surfaces.
-Steve Dunlop
Minneapolis, MN