I just got mine off ebay from a sketchy seller. its front focusing element was loose and it was full of dust. i see your ring cover is already off exposing the three screws holding the glass on. Dont be afraid to pull it apart and lift the front glass off the lens, it just sits there on its own mount. Theres no calibration needed when you put it back together. Its an easy fix, get some good small screwdrivers and pull it apart, clean it out and put the lens back together. Easy fix. No calibration needed.
definitely worth a try, as it sits its worth garbage, repair is same whether u try it first or send it in.
and if you fix it then u can feel better about selling it for more money.