If your transmission is leaking gear oil and "marking it's territory" on your garage floor then it is usually caused by one of three seals failing.
Leaking at the rear of the transmission:This is the most common type of leak and is caused by the clutch arm boot failing. To replace it you will need to disengage the clutch cable at the left end of the clutch arm. An easy way to disengage the clutch cable is to pull in the clutch and then stick a piece of wood in between the lower portion of the clutch arm and the exhaust. Then remove the piece of wood so that the clutch arm falls away from the boot. Then unscrew the hose clamp that holds the boot on and replace the rather expensive rubber boot. (Part 23131338731)
Once you've replaced the boot be sure that it makes a good seal on the nipple on the right end of the clutch arm when you re-attach the clutch cable.
Leaking at the front of the transmission:
The transmission can also leak gear oil out of the drain hole in the bellhousing. (If it's gear oil then it should be clear and have the rotten egg smell of sulphur. Motor oil will be black and not so smelly and is covered in the
K bike clutches thread.) There are two seals that can fail that will leak gear oil from the front of the transmission:
Input shaft seal: This is the seal around the transmission input shaft. It can be replaced by removing the transmission, picking the old seal out and tapping the new one in. (Part 23121451151)
Clutch pushrod seal: This is a small seal at the rear of the clutch pushrod that keeps gear oil from traveling up the center of the input shaft. The way to diagnose if this seal has failed is to remove the transmission and inspect for gear oil on the clutch pushrod. This seal has a metal collar with a very tight tolerance and it takes some work with small tools to pick the old one out. Install the new seal using a hammer and a socket that's roughly the same size to tap the new one in. (Part 23211451159)
