This was on a 1989 R100GS with 52,000 miles. Pulse air system in place. You can see the face of the valve beginning to crack; here are two better pictures of the valve itself. Click for close-ups.
|R90, R100 32mm*||EX||IN|
|R1100 to 10/95||EX30°||IN||6|
* '77-84 R100 models with 32mm carbs
** '77~84 R100 models with 40mm carbs