The main condenser, in the round aluminum "can" has two lenses and a corregated aluminum spacer. I suspect the two lenses are identical, but if you assemble them in the original positions, all will be well. To take it apart, remove it from the enlarger, hold the can sideways and tip the top lens out, then you can get the spacer and lower lens. Do this on a table or workbench padded with a towel or something, just in case. Water and ammonia should be fine for cleaning them. When you re-assemble, the convex sides face each other.
As for the lens, El-Nikkors, Componons, and Rodenstocks get all the attention nowdays, but there are lots of other excellent enlarger lenses around, and you can't go strictly by reputation anyway. The only real way to tell how good it is would by to try it out.