I was pulling apart my bike today cleaning it for a paint job and came across this gunk when I took the end off the drift shaft.
It looked like rust or old dried grease but after drowning it in degreaser I came across metal filings. Should I be concerned?

DEFINITELY. The splines look well worn, i would remove drive shaft and clean  /check splines.

Clintinz wrote:It looked like rust or old dried grease but after drowning it in degreaser I came across metal filings. Should I be concerned?

Don't worry, there's more where they came from. 

That is an excellent photo. Take another with the camera angled so the end profile of some of the splines' ends can be clearly viewed. If their points are chiseled on one side like a saw tooth when viewed from their ends, mileage on them will be limited but I can't tell how much wear they have. 

These are worn but not worn out.

Thanks foe the info. After a good clean up it came away looking like the attached. Tell me I still have life left in it?! Fingers crossed

Those don't look too bad.  I like to look at the flat on the top of the spline, the wider they are the better.  As the splines wear, they get narrower until, when they finally fail, there is no flat top surface visible at all.

Phew! I’ll grease them up and put it back together. Thanks guys

Just stick to a yearly regrease with Castrol Optimol / Straubags / whatever and they should go on for quite a while yet.

Looks like the problem was on the drive shaft instead. If what you say about the flat tops still applies to the shaft then this looks bad

Yeah, that drive shaft has maybe 100 miles left in it if you are real gentle on the throttle.

A brand new one is $383 at MaxBMW. If you're not in a hurry, you should be able to find a good one on eBay for $200 or less.

Hi

Unfortunately your splines are starting to wear out.
How long it lasts you depends on how you ride your bike.
Thrash your bike and they won’t last much longer. If you are gentle with the throttle, you might get many more miles.
It’s up to you.
Make certain your clutch arm, located at the back of your gearbox is greased up.
If not, your clutch cable will snap and replacing it won’t fix the problem unless you also grease the clutch pivot arm.
Good luck.

You can fit a grease nipple to the clutch arm.
Regards Martin.

Point-Seven-five wrote:Yeah, that drive shaft has maybe 100 miles left in it if you are real gentle on the throttle.

A brand new one is $383 at MaxBMW.  If you're not in a hurry, you should be able to find a good one on eBay for $200 or less.

Given that buying over seas in NZ $ then paying shipping it going to come close to $1k and i can’t find one locally. I’m thinking of replacing the whole back end from the gear housing, swing arm, drive shaft stand etc from a k1100rt. This would be similar price (Which I can find locally) and I can fit a larger rear wheel. Question is… can my existing alternator, starter motor and rear diff fit on the k1100rt back end?

Starter motor and alternator, yes. Rear diff, no. You'll have to get the complete rear end, from the bell housing back.