Alan,
Some chemical paint strippers (paint removers) are more aggressive than others and do not affect plastics in the same way. Polyethylene, probably what the scopes are made of, is a fairly solvent resistant plastic and is more tolerant to solvents than other plastics. Offhand I don't know which paint remover you should purchase, but I would look at the labels on paint cans in the hardware store and select some of the milder solvents, such as benzyl alcohol. Alternatively, purchase the smallest quantities available of a range of removers (where the ingredients differ) and test them on the polyethylene before you do the real job.
My moto, use the least abrasive and work your way up, and take your time.
Ron