depends if you are getting a good deal on a benz then go for it, if its on front wheel wall thats fine, cus you always replace the fender with used one or new one, but if its on quarter parnel then its the problem, you can fix the rust with bondo and stuff or as someone says cut the metal and put new metal sheet on it, but not worth it cus the cost to do on the fender is better to replaced for cheaper one ...