Vintage BMW Motorcycle Owners

Attaching a photo of what I noticed today after a ride. Looking to members for possible causes. Thanks.

Have you done any maintenance back there lately? Ever happen before?

Looks like the grease used is not suitable and has gotten hot enough to melt and flow. Should be a good/decent wheel bearing grease with moly included.

Looks like your brakes are dragging overheating the drum
I had the same problem with my r51/3
When I reinstalled the brake lever it was 1 notch too high so the brake lever was acting like a foot rest and putting a slight drag on the rear brake overheating the drum
Relocated the brake lever down one notch and all is ok now
Tommy

Appears to be the wheel bearing grease leaking past the bearing seal; Kurt's got you on the right track, and asking you the right questions-

/2 wheel bearings have been pretty well established as perhaps the strongest components of the bike, well overspec'ed for the application.
Given proper maintenance, they should outlive the rest of the bike.
Proper maintenance includes proper adjustment/lubrication/protection.

Grease is a lubricant (oil) suspended in a sticky goop (known as soap) made to reduce/prevent roller/race contact, and stick in place as the bearing spins.
Some of the ways greases fail is by age, or being subjected to excessive heat, or subjected to contamination, or simply being used incorrectly, or some combination of the above.

Age- Old grease will separate if given enough time, the soap will harden, the oil will simply leach out, and drool past the seal.
Our /2 instruction manual tells us to remove/clean/repack the wheel bearings every 8000 miles.
Doing so would certainly prevention prevent grease failure due to old age, (assuming the bike gets ridden) though that's certainly more often than I get around to it.

Heat- Excessive heat will break down grease, the oil will separate.
Grease is not a coolant, grease will store heat it's subjected to, Tommy gave a good hint: check for brake drag.
The /2 rear wheel will always run hotter than the front, so it might also be good to also check that there's sufficient oil in the rear drive.

Contamination- The bearing seals have two jobs; keeping the grease in the hub, and keeping contaminates out.
Both the early felt and the later rubber seals will do the job, provided they're in good condition.
Good also to check the drum side seal as well; if that's leaking, the brake linings may become contaminated.
Another type of contamination is mixing greases that are made from different soap bases, which can also sometimes lead to oil separation.
When repacking bearings, repack with the same grease as last used; if the previous grease is an unknown, then a thorough cleaning of the bearing is wanted before repacking with a different grease.

Incorrect use of grease- This application calls for wheel bearing grease, so be it synthetic or regular, or even marine, use a wheel bearing grease.
Some prefer marine wheel bearing grease because it's formulated to withstand submersion in water; (for when offloading boat trailers) so kind of a belt and suspenders approach when used on a /2s.
When packing bearings, some choose to pack the wheel hub itself solid with grease, I'm a proponent of packing the bearings, but not filling the hub itself to capacity, I see nothing to be gained, and doing so will will retain more heat; but again, each to their own.
Best-
George

Appreciate the generous replies. Will investigate with the insights from above. Thanks so much.

Let us know what you find
Tommy