Hello Neil,im pretty sure the seal is actually closer to the diff itself,your probably used to the norm jap or LR axles with seals at ends and full of oil,I think front axles with UJ's are designed like that because the shaft ends (UJ end)don't stay central in the tube when your turning (unlike a CV joint )
get some of these http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR0.TRC0.H0.Xjeep+axle+tube+seals.TRS0&_nkw=jeep+axle+tube+seals&_sacat=0
to clean the axle out, get a thin broom handle and screw a large penny washer to the end ,the scrape the crud out
Get rid of those bits of plastic when you fit the tube seals
Stopping all the muddy water getting in the tube means you will have to replace the inner seals less often which saves the hours of labour involved with taking the front diff out.