turbobenz, the reason a seal goes out is that the manufacturers use a spring-backed neoprene seal to prevent all oil leaks, because customers hate oil leaks and will make warranty claims to correct them. The problem with the neoprene seal is that, although it seals really well when new, after a zillion heat cycles it gets hard. When it does that, it will sometimes break, and the broken end will dig into the shaft, but more often it won't break but will just cut a groove in the tail of the crankshaft, or the transmission's input shaft, as the spring drives the hard seal into the metal. When you replace a seal like that, you can press a thin metal repair sleeve over the shaft, although it is a little tricky to do and sometimes the shaft has to be turned down first. What I prefer to do, however, is to simply not quite bottom the seal out in its carrier when I press it in. The groove in the crankshaft or input shaft is only about 1/8" wide, so if you leave about that much space between the seal and its carrier when you press the seal in, the seal will be contacting the shaft slightly farther out, where the metal is still there. Some people are afraid to do this because they fear that the seal will fall out of its carrier if not bottomed out. This is not true because the only forces acting on the seal during engine operation are radial in nature.

The manufacturers could use a different seal material that would last virtually forever, at the expense of minimal leaks, but their customers would hate the leaks too much.

Now, turbobenz, I suggest that you go float up some hills (inside joke).