Hi All -  not been on the site for a long time but now spring has risen - time to wake up the K75 Ultima with a MOT and service. This bike which some you will remember for the initial problems has now completed 88,000 miles (140000K) and over 20000 miles since the problems were fixed. Faint hope ! Anyway, on removing the Bevel box I found a good dinner spoon of oil in the joint area between the bevel gear and the swinging arm. Has the oil seal in the gearbox leading to the Cardan shaft failed or what other reason for the oil there? As far as I know the gearbox rear oil seal was original.  I made the mistake of putting full synthetic GL5 oil instead of GL5 mineral oil in at the last service a year ago. 
Is this possible reason?
Can I just drain the synthetic oil and refill with hypoy mineral oil ?
Anyway, If I must, can I replace this seal without removing the gearbox : the problem being I cannot find any instructions in Haynes of Clymer how to go about it.
PS the front seal towards the clutch was replaced with the clutch plate 2 years ago, and also the gearbox breather cleaned.

Sorry for the long story but thanks in advance to anyone who can assist me.

Regards
George

Now that we've all arrived in the 21st century together, posting photos of this condition would add some clarity, for me anyway.   

I believe that oil is likely to have seeped past the final drive pinion seal rather than from a gearbox seal unless its path from the gearbox can be tracked. I personally wouldn't get exercised by that much oil in the area of the final drive input shaft if that is all that occurs within 6K miles of riding, which is approximately how often I replace final drive oil and lubricate the final drive's splined shaft. That would depend on the size of the dinner spoon—papa bear, momma bear, or baby bear. Eventually though, action will be needed.

Here is a link to a post explaining the procedure of pinion gear seal replacement—if that is the source of the leak—as completed by somebody not using BMW special tools. The process starts at Reply #3. In my Clymer's manual, seal replacement procedure starts on page 408 under the heading Overhaul.

I doubt that your choice of gear oil has anything to do with the leak. Why don't you change back to your favorite gear oil and find out if there is any effect?

If it's coming from the transmission then there shuold be oil traces in the swing arm and oil in the boot at the front of the swing arm.

But it's usually the seal on the FD.

My experience would say it's the seal on the pinion shaft of the final drive. Just monitor the oil level and if there is a big change then act. I have seen many like that but never a big failure.

Hi George,

As others have said, just monitor the situation for now.

Should you need to change the pinion seal, then The BMW Club UK has the tools to do the job (available to paid up members only though). 

Mike

Hi all,  thanks for all the assistance. However I am a little bit confused as I did not think the oil would migrate upwards from the bevel box.  But it would seem I may have been wrong there.   I have now dumped all of the oil from the gearbox and bevel and refilled with mineral oil as I still have original BMW Oil seals in the gearbox. 
I will use the bike for the next month - forecast snow and ice permitting -  then extract the bevel and check.  Will proceed from there.
Anyway - thanks again and -  case continuing!
This section does not allow photos to be posted along with questions.

Regards
George

George R wrote: This section does not allow photos to be posted along with questions.

As far as I know, this section and most other sections does allow photos to be posted with or without questions. The process for posting photos from computers and phones or from Web photo hosts is in the Functionality section. It takes some practice.

My K100RT final drive was like that when I was doing the rear main seal but I did all the seals as it was apart.

I was thrilled to find that particular leak you have because it meant the splines of course were in perfect condition.

the thing you may have to think about is the migration of the oil from the bevel box  past the seal , washing all that good molly lube on the splines away on the drive shaft

have a similar issue I want to resolve soonish

good luck

Hi charlie99 and others - I was lucky - the oil had not reached the splines and the Staburags was still ok. First t ime I have used it and am much impressed.
Made a tool I was wondering if any of the K clan would be interested in - it allows the timing gun to focus on the marks and leaves one hand to adjust the marks. If so could someone help me to post the photos? Never done this before.
Thanks in advance
George