The lock washers were the original problem, they would crack, fall out, then the bolts would be loose .
The bike didn't come from the factory, someone familiar with older airhead bikes, must have performed maintenance on it, and put it back together with the older version of bolts .
I would order the newer short bolts, and install them without any washers .
I checked BMW parts sites (even the official BMW site), and all of them show bolts and washers, anyone know the correct part number for the short bolts ?