Had my '09 SERG all shined up and recently serviced by the dealer as I'm off on a trip the end of the week. Late Saturday, I found a small puddle under the tranny which, sure enough, was tranny fluid. Talked to my service manager (Kirk at Bartel's HD), a very good guy. He said its a common problem and told me to check the two bottom bolts of the transmission side door (#'s 2 & 3 in the diagram below). They were loose enough to finger tighten!

So much for checking your "critical fasteners" at a dealer service. So, I removed the bolts, cleaned them, applied blue loctite and reinserted. Not nearly enough room to use a torque wrench (with out removing exhaust) but specs are 19 - 26' lbs. Tranny took about 3 ounces of Amsoil Gear Lube.
My friend Fred says he has been through this with his '09 SERG and another '10 Road Glide. Kirk calls this a.m. to check on me to make sure I'm fixed and tell me he has a bike at the shop where the owner did not notice the leak and now may need a new tranny.

I went to OSH and found on sale a GearWrench Micro Kit ($12.49) that has an allen driver that will fit in between the tranny and exhaust, just in case this happens on the road.
Searched and did not see this on the forum but now I know of four bikes with the issue. Might be worth checking.