Is my final drive going bad?

[StatiK]

I picked up my 2007 R1200RT a month ago with about 31k miles on it. When buying it I checked out the final drive but turning the rear wheel slowly in neutral and felt no tough spots. I torqued it top to bottom and side to side and felt no wobble. When I first got to riding I perceived some road noise sounding like it was coming from the front. I concluded this must be the road smart 3s that had not worn very nicely resulting in a bit of a bumpy condition on the center of the tire. I also notice that when leaned over decently in a turn, either side, there is a strange whirring noise that, were it heard in a car, one might attribute to a poorly worn tire or a bad wheel bearing. Now I wonder if this road noise is indeed the fault of the tires or if it might be the final drive.

After putting about 1k miles on the bike I finally got around to changing the final drive fluid. Before removing the wheel I checked for play again and when putting in a little more force than I had before, I did perceive a very small amount of play. Not enough to be visible but only enough to feel. As soon as the wheel came off I could feel that the hub was a little notchy to turn by hand. Not terribly, but not smooth either. Once the final drive was turned down and draining and the driveshaft was disconnected the notchiness remained. The fluid was a little darker than I would have liked to see but there was no significant sediment. The magnetic drain plug had some sludge accumulated on it perhaps equivalent in volume to two grains of dry rice. The rear drive shaft u-joint was just about as smooth as I could have hoped it would be. I greased the input shaft and replaced the necessary seals and topped it off with as close to 180ml as I could get in there of 75w90 Amsoil severe gear. Big Amsoil advocate. Did a test ride of about 13 miles and all seemed the same as before. The final drive does and always has felt rather warm to the touch after a ride but never hot. This is my first BMW so I'm not sure what's normal.

So, questions. Is my final drive on its way out? Do I understand correctly that the 2010-2013 vented unit is a direct replacement for my 2007? It appears that that is the standard BMW replacement part. It also appears there are a couple different improvements to the 2010-2013 units making that worth while rather than having this unit rebuilt. Can anyone weigh in on that? I see used later model final drives going for as little as $450 on eBay. Another question is how in the world do you get the final drive boot properly seated on both the swingarm and the final drive? Getting it seated in the swingarm before tilting the final drive up is easy but all I can do is massage it a little to try to get it to pop in at the rear and I don't think I've been successful. I appreciate any assistance in advance.

[simbo]

I'd put it down to the tires, from the final drive checks you've done all seems okay.

[Stu]

What tyres are you using?

[Fourbears]

Once my Michelins RP 5’s and 6’s wear then I get a humming noise from them. Once changed it went so that might be what you have. Change the tyres first I’d say then see what you have.