If I remember correctly the 300tdi defender's front prop is almost full closed in normal running position. The splines move far less than you expect on normal set up I can't remember but I think it's something like 10-15mm going down and 0-4mm going up. Personally I would separate, clean, grease evenly then put it back together I would then grease it through the nipple then put it back on and grease it again. I wouldn't worry about it to much you clearly look after your truck more than most do so it will wear slowly.
Mike