I bought a ol 5519 and can't figure out the rheostat. Nothing on the pin housing turns. Plus is the only thing covering the wrapped fibre this Mylar tape?
Are you sure it has a rheostat? They make a model that doesn't. If it does, the entire smooth front on the sight housing is what spins and covers the fiber (or uncovers it). In this pic it's the part with the sticker on it.