That oil leak is usually an indicator that the bearings in the final drive have gone walk about and you’re now grinding metal bits. Fortunately, this is not that kind of oil leak.

True enough the final drive on my GS went south last year, spewing oil all over the rim in the process but it was replaced and all was well. Or so I thought.

My first trip out after the replacement I noticed gear oil dripping down the side. I took the bike back and the shop had a look at it saying, “Don’t worry, the unit was just over filled and some of the oil is leaking out the case vent.”

So I didn’t worry. I road it. Naturally the oil left a sticky residue on the drive and it acumulated a black sludgy mess. So last month I give the bike it’s semi-annual bath and clean up the final drive really good.

Please with myself I took it for a spin. I stopped for a break and glanced at the final drive. WTF?! Oil was leaking down the side! Still!

So I did what any good netizen does. I went to my message board of choice, and posted a note. The response boiled down to two issues:

1. I got water in the case while washing it, and it was being expelled out the vent with a little oil.
2. The rubber O-ring around the ABS sensor may be torn.

Since I’ve put about 70K miles on the bike, giving it a bath twice a year, I have never had problems getting water into the unit. I hand wash it so water isn’t being forced in by a presure hose.

That left the O-ring as the culprit. I picked up the part, along with some additional crush washers for the filler screw, and made arrangements to borrow my sister’s tools. (It’s good to have a mechanic in the family.)

I first cleaned up the drive unit (again). Took the funky BMW “mud-flap-thingy” off and unscrewed the ABS sensor.

Imagine my suprise when I discovered that I didn’t have a torn O-ring. I had no O-ring at all! You can clearly see in the picture the channel in the case where the O-ring is supposed to go, but there wasn’t one in there. That would explain why it was leaking.

I lubed the new ring with a little gear oil, popped it in there and slid the ABS sensor back in place. For you neat freaks out there I did clean up all the screws and shims before I reassembled everything.

It all went back together good as new. I topped off the oil in the final drive, which suprisingly only took maybe a couple teaspoon fulls, and took it for a spin.

No leaking! I always love it when something goes right.

Cost to fix:

• O-ring: $1
• crush washer: $.40