I bought my R850 used with about 19,000 miles. Judging from the rusted screw and bolt heads, the previous owner did not garage the bike. Perhaps this also had an effect on the muffler baffles. Whatever the cause, the baffle is rusted out right where it exits the muffler. This photo is of the end of the muffler. The rust colored part is the inside of the tailpipe. The black gaps are where the baffle/pipe has rusted away from the stainless steel case.

BMW has changed this design a bit, and for good reason. The muffler/catylitic converter is stainless steel. However, in a bizarre twist, the baffle inside the muffler is regular steel. I would love to know why. After market mufflers like Staintune are stainless inside and out.

From below you can see that the rust holes are not so bad at the top of the inner pipe.

The right side is rusted through also, although not as bad as the bottom.

The left side is also rusted through. This muffler is loud. Accelerating from a stop to 30 mph the noise reverberates around inside my helmet. It isn't cool, it is just irritating.

The BMW stock replacement is around $1000. That's a crazy amount for a muffler. Aftermarket mufflers (including a catalytic converter replacement pipe) vary from about $435 to $1200. Some of those replacements have a lifetime warranty. However, I'm told that aftermarket mufflers are universally louder than stock, and many of them have second rate construction.

I'm not ready to spend that kind of money, so I started looking at fixing my muffler. Stage one of the quick fix has already been done. I cut a short length of pipe from a VW aftermarket exhaust I had laying around. You can probably pick up a suitable short connector/adapter pipe from you local auto supply store.

The pipe inside curves up and then down, so the patch I've inserted is only about 1 inch long. I pre-drilled a small pilot hole in the patch pipe.

With the patch in place, I drilled up into the baffle, and put in a sheetmetal screw.

YOu can see that the major part of the rusted gap is gone. However, the patch is not really a tight fit. This has already made the muffler quieter.

The next phase of the project is to pull the pipe off the bike and MIG weld a bead between the patch and the stainless case.

I could probably weld the muffler on the bike after disconnecting the battery, but I don't want to risk stray electrical current from the MIG frying the bike's computer (or anything else).

I'll post photos of the final welded fix.