The previous owner probably committed the unforgivable sin - squirting something like WD-40 into the iris assembly. Pure alcohol should just evaporate. Try gentle heat from a hair dryer. The trouble is that the spots on your lens may be diluted WD-40 solution, that is they contain oil, rather than just alcohol. In this case you'll maybe have to dismantle the lens to clean the glass - but try and dismantle as little as you can get away with, more chance of having a working lens at the end of the exercise!
If you were able to get at the iris, can you reach through with a cotton bud to get to the spattered lens surface?
If so, use some pure cotton wool, roll your own cotton bud by pulling a small tuft off with a damp wooden stick (cocktail sticks are good) and rolling into a bud against the plastic bag. Don't touch with your fingers. Dip in pure alcohol and, starting at the centre of the lens, work gently in a spiral to the edge. Discard the cotton and roll another. Repeat as many times as you need too (maybe a dozen). Washing a lens like this is much safer and more effective than rubbing with a cloth...