Motorcycle Repair: Transmission seal leak, vent hose, gene gene

Question
Previous owner overfilled with tranny fluid. Had the bike checked and it has a blown seal. How do I check if the vent hose may be  plugged? If I need a seal, about how much in your experience should this cost. If the seal is bad, will heavey gear oil slow the leak down? Thanks, gene

Answer
Gene before you do anything drain the tranny and fill it with 80/90 gear oil, only 22oz.  Clean off the BACK of the inner primary with brakekleen and wash everything off good.  Then run it and check for leaks.  What happens with an overfilled tranny is the excess blows out the breather hose and down the back of the inner primary, making it LOOK like a tranny mainshaft seal leak.  I've never seen a seal blow just from overfilling and I've never seen a vent hose plug.  At least this will let you see if you really have a seal leak.  If you do it will cost about 2-3 hundred.