Bike is '85 K100RT

Oil leaked from fd onto wheel/tire/pavement.
Spoke to previous owner & learned not all seals replaced when apart for spline lube.

My question: what parts should I order to fix leaking fd?
I want to have the necessary parts before dis-assembly.  



Thanks in advance for any and all replies.

Troy

Anyone?

Am I asking the wrong question?
Am I asking in the question incorrectly?
Am I asking in the wrong forum category?

TIA,

Troy

First you need to determine where the leak actually is.  Front seal usually will leak from the joint between the drive and swingarm.  The big seal which is covered by the wheel will leak onto the disc and will be easy to determine if the wheel is removed. Third the oil can escape from the breather which is right on top of the housing rearward of the caliper.
The rear seal would be the most likely but to start with check the oil level which should be level with the bottom of the thread of the filler hole.
Get your VIN and go to Real OEM.com and put the last 7 digits into the serial number box, click search and it will tell you the year/month and from that the correct drawings come up with part numbers and seal sizes etc.

http://www.realoem.com/bmw/enUS/select

I had a similar issue with my '85 K100RT.

In my case it was the seal where the final drive output comes through the housing, item 1 in the diagram at http://www.realoem.com/bmw/enUS/showparts?id=0504-EUR-06-1985-K589-BMW-K_100_RT_84_0504,0505,0514_&diagId=33_1565   As Rick says, that is the most likely culprit for you, too.

Since I was going to dismantle the drive, I also ordered and installed the equivalent smaller seal on the input shaft and the large O ring that seals the two halves of the housing at the join. I would recommend you do the same. Drain and filler cap sealing washers as well.

Clean and carefully inspect the surfaces that rotate inside the seal. Hopefully, there will be no issue, unlike a tractor mounted post hole digger that I am renovating for my son. In operation, it is identical to the K100 final drive. Badly pitted surfaces have given me some interesting work, but it is much less of an issue if there are small leaks happening in that case.

Ideally, you would check the backlash with the gear meshing, and adjust the shims (as in add, subtract or exchange) on the input and output shafts. This also assumes you have spare shims of different thicknesses on hand for the purpose. In practice, unless there are noises or other indications, most of us normal people just take care to not lose them and replace them as they were.

Bill

Many thanks for the replies.
Very much appreciate you taking the time to help this newbie to brick bikes.

Regards,

Troy

August 2016: 68k miles Mine leaked at the vent of all places, due to the oil running extremely hot. Changed the oil even though it was fresh and the problem resolved. Never found out the cause.

February 2017: 78k miles Did a major job, clutch rear main seal etc. Also new seal to the final drive.

April 2017: 80k miles Felt all was not right and ran a check on the final drive again. Got second opinion, it was barely perceptible...big bearing replaced and problem solved. Also this was the cause of the problem previous August.

89k miles now and all is well.

If you suspect something don't leave it or you will lose the bevel drive as well.