The outer tube seals help keep junk out...and keep junk in The inner seal (pumpkin) keeps the gear oil in the pumpkin. (assuming we are talking about a dana 30 or similar).
The outer tube seal theoretically keeps junk out of the tube. It will also keep junk in if it is able to pass through. Granted, it is hard to have things pass through.
I have some Alloy USA's on my Dana 30. One came loose and the seal that presses the whole thing into the tube wore down. They would not warranty it. They said it was install error (4 wheel parts). I used some RTV adhesive to jam the sucker back in with no issues since. My tubes were clean when I did the re-install.
The rubber seal that goes around the axle shaft is worn, but I will leave it to the next owner to replace. It is a part that can be replaced.
I am building a front Dana 60 that came out of a mine truck. It's outer seal had blown. I scraped wads of junk out of the tube. Did it stop the shaft from turning. No. Did the fluid I drained from the pumpkin look horrible - yes. I cant't say what if anything migrated from the outer to the inner, but the Ford Dana 60 is built with an outer seal and an inner seal.
I don't know about that but if I say something is crap its probably true.
One person's crap is another person's treasure
I'd have to agree, that's why we are always on this threads, to give and get info. But I don't understand why no one wants to buy jeeps for eleventy billion dollars, can't remember if that's the amount Anti posts