Kinda late to this thread, however I just completed adjusting my 1978 R100S sidestand to where it will remain in the down position.
This link offers the how-to info: Duane Ausherman mentions that BMW altered the sidestand function in 1972 to counter a lawsuit.
http://w6rec.com/duane/bmw/sidestand.htm
The excrement in
my punchbowl was the spring attach tab had a bend forming a tab that prevented me from rotating the attach bracket. A long draft and careful love from a ball peen hammer fixed that. I'm not particularly altitude-challenged with a 32-33 inseam but the location and self-retract sidestand was
formerly a bother.
The yellow arrow points out the "modified" spring attach bracket. It has been bent -using a long drift and hammer- away from its normal position; that being snug against the chassis and preventing the fix. After moving it and loosening the 19mm motor mount nut, the bracket self-positioned itself when the sidestand was swung down. Don't forget to tighten up that big nut.
Another view. I'm pleased with the result plus my opinion of lawyers continues to be reinforced.