I have a 1972 BMW R75/5. I am attempting to restore it, but am missing a very important bolt. It is the allenhead bolt in the center of the left air filter housing. The middle picture: http://www.slash5.net/slashmn/pg66.jpg I need to replace it and found a guy that will send me one for free if I can just figure out what the size/specs of it are. Please help!