sorry but i think you will have to. i had that problem on all the benzs and only on the benz's, i think its cause the OE glass is too soft, rock chips and wiper arm marks on glass is not good.

I tried glass polishes, etc. and none worked. I ended up replacing my glass with aftermarket, I am happy with it, it looks good, stands up to rock chips better and no wiper arm mark. And parts and labor is still a hundred bucks cheaper than the OE glass itself. Goodluck...