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[J.D.]

For those of us who own the older Twin Cam motors, I'd suggest checking your shifter shaft seal.  The older, single lip seal design is prone to leaking and seems the rubber used is getting to that age where it gets harder and less flexible.  On my 02 I have been seeing the gear oil weeping and mistakenly originally assumed it was from the mainshaft area.  It's somewhat of a safety risk as the oil seemed to really weep out most at speed, and it runs right down and ends up on the left side of the rear tire tread.

The seal has been redesigned with a more robust double-lip style.  It's a bit of a PITA to replace this $4 seal as the complete primary needs to come off, but while it is off it's a good idea to upgrade the inner primary mainshaft seal and starter jackshaft seal as these have both been redesigned to the double lip style.

[Twolanerider]

The Cometic seal has also been a much better than the original stock option for a long time also. 

[J.D.]

Yes the new OE and Cometic are very similar and both a much better seal design than the original.

[Twolanerider]

Yes the new OE and Cometic are very similar and both a much better seal design than the original.

The occasional refresher is never a bad thing.  Even the issues known for years with solutions from the aftermarket for nearly as long can be forgotten without the occasional mention.

[ultrarider123]

I'm not sure when they upgraded the shift shaft seal (say that three times fast....) but my '09 SG, '12 SESG and my '15 SERGU all had factory shift shaft seals leak which called for replacement under warranty within the first year of ownership on each bike....

[J.D.]

Good comparison photos of the old vs. new seal design (inner primary and starter jackshaft are similar in principal):

[J.D.]

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