OK, I have found the answer, this by-pass check valve opens when the oil filter is plugged. God knows how long it's been like this. Fellow Heads, put this on your to do list!
Looks like it may be a bitch to remove especially since someone earlier tried and failed but it must be done.
Any suggestions on removal would be gratefully accepted !
parts to replace are BMW #'s

111 11 250 159
071 11 986 280
111 11 250 157

will be checking that with every oil filter change from now on!

Still pondering the best way to get this done. Anyone with experience regards this task? suggestions would be helpful. Did you use heat to help unscrew? Lay bike on side? Remove entire canister?

I see that you are not getting any replies on this topic. I have never had this exact issue on any of my bikes. If you have not already done so, find "snowbum's" web site and read all about it. http://bmwmotorcycletech.info/

As a general rule, heating a screw or nut can help release a resistant screw or nut, but if it is staked or otherwise "set" in some way, this will not help.

Yes thanks, even Snowbum does not have much info on procedure. Was hoping someone had more some tips. It's gonna be a winter job, I'll report back.
Best thing the parts cost under 10 bucks

Sorry, I've never done this job. But I have lots of experience doing weird repairs on other engines.

I'm trying to envision this part, and the parts fiche is exactly no help at all. Is it in the end of the oil filter "well" where it's a straight shot ? Photos would really help.

Here are some tips for these type situations....
• This may be obvious, but you just get one or two shots, so you need to think through all your steps before beginning. Once you start, you are totally committed.
• If this is an aluminum or brass screw, then you cannot use an Easy Out type extractor.
• Pushing inward to engage the "screw" during the entire process is actually more important than turning the "screw". Slippage is what tears up the screw head and makes the job impossible. Working with gravity is always best, so laying the bike over always helps.
• Hammer the special bit into the old screw head to get 100% engagement before you start rotation.
• Count on destroying the old screw. Having the new replacement in your hand will 1) allow you to configure a correctly fitting tool for extraction, 2) know which direction to turn the screw, and 3) know the correct drill bit to use in case all else fails.
• Don't cheap out, count on buying the best quality bit and then grinding it to fit the replacement screw exactly. If that's the only screw it ever turns, then it will be worth it !
• If you have to drill, then having a second person with a vacuum cleaner is really helpful. Duct tape a 12" piece of 3/8 hose onto the vacuum snout to get right up next to the point of chip creation.

Hope this helps.

Thanks for your tips Wob, since the oil filter's not doing much with this situation I'm just gonna dump change the oil every 1500mi. and keep ride'n till snow fly's. A....'Winter Project", which is not too far away in this State O' Maine!'

Brook Reams did a very nice write-up on this by-pass valve. It includes removal, diagnosis, repair and re-installation, including pictures. Check out this link to his article:
https://brook.reams.me/bmw-motorcyle-rebuilds/1983-bmw-r100rs-rebuild-project-index/11-bmw-r100rs-diagnose-intermittent-low-oil-pressure-light/

Wow! thank you so much Murph...... didn't come up in my related search's

Update.......did not go like it looked in the brochure ..we could not get the set screw out. Heat and all easy out try's failed to budge it. This R100T has over 100k miles so, I'm just gonna keep on ridin for now!