Check this post. http://advrider.com/forums/showthrea...88#post8436288
Since this post both OEM straps have fatigued and broken. Now I have a 1/8" band iron top strap and an aluminum lower. I will someday make another aluminum one so they match.
And yes I have a R100GS. Bought it brand new at Andy Pelc's in 1988. It was my first BMW. It's a real jewel.