>>Cap of rear brake reservoir?
>>the plug to the left of the access plate number?
>>point of entry for injection molding of a plastic part
>>Tip of an axle slider not finished off properly
>>Inner air box cover?
Nope
>>Casting dimple on frame?
Nope
>>ok I think we need a hint.................is it on every Buell, or possible
>>Mod/aftermarket?
To my knowledge, found on every stock Buell (except maybe the Blast).
>>Best I can figure is its a Frame or swing arm peice.
It is not part of the frame or swing arm proper, but the big hint is that it is LOCATED on the swing arm!