Originally Posted by quadrunner
Just as I was returning home from a ride today on my "08" LT I noticed that the rear brakes weren't working very good. When I pulled into the garage and parked the lady I started to inspect her and I noticed a fair amount of what looks to be like gear lube on the rim It was dark grey in color, and as I looked around a little further and found that the oil seemed to be dripping from the rubber boot on the drive shaft. I haven't taken off the tie rap or clamp yet, as I wanted some opinions as to what it might be. The bike has about 9500 miles on it and the gear oil was changed last year.
If you think it is leaking at the rubber boot, loosen the boot and see how much lube runs out. Put a container under to catch the lube.
If a significant amount of lube comes out, it is coming from one of two places, either the final drive or the transmission.
The final drive lube level is easiest to check, just remove the filler plug with the bike on the center stand. Wait a few minutes for lube to run down off the gears. The FD lube level should be near the bottom of the threads of the filler hole. If it is low, add enough lube to bring it up to the bottom of the filler hole. Measure how much you have to put in. If you have to put in more than a few cc's it maybe that you have a leak at the FD pinion seal.
On the other hand, it is not unheard of for the output seal of the tranny to leak, Past suggestions have included putting different color lubes in the tranny and FD so the color of leaking oil will reveal the source.
Searching the site will reveal past posts about leaks into the swing arm.
However, I'm surprised that much oil from a leak into the swing arm would get onto the rear brake rotor, but then I've never experienced it so can't be sure.
The other possibility is a leak at the hub seal behind the brake rotor. A leak there for sure will lube up the brake rotor and affect braking. Again, checking final drive lube level will suggest if the FD is leaking.
Another thing to do is to drain the final drive and look at the drain plug magnet for metal on the magnet and metal in the lube. That would indicate FD bearing problems.