I have an R90 2.8 Elmarit that has a messed up rear element. It takes great photos, but it bugs me, so I bought a bgn R 90 Elmarit in the hope of swapping the rear elements. The elements came out fine, but the tolerances are different from lens to lens, so the new rear element didn't want to easily go into my old lens, so I put everything back and decided to just give the bgn lens a try. Trouble is, that one has some oil residue inside the front element. Not a lot, but I'd like to clean it. Does anyone know how to remove it? There's a ring around the front that has a small screw, but I think I removed that front cover once on another lens and could see no way to get the element out. Maybe a suction cup deal? Anyone ever had one of these apart?