If the job was done well, I would say what's the difference - you have some part of the car that is newer than the rest, that should normally be a good thing. All this angst over spot welds and fender notches I find a bit silly myself. It's perfectly normal to have some parts replaced from time to time, be it due to wear (exhaust, tires, oil, filters, shocks, starter motor, alternator, clutch, light bulbs, coolant, battery, spark plugs, points, injectors, barometric compensator, thermostat, door whiskers, maybe some upholstery - it's a long list of things that by definition will not be 'original') or due to some minor damage like a fender bender. I think I would rather have a car that had its fenders expertly replaced with "original Mercedes" parts, than one full of invisible bondo to repair now-hopefully-dormant rust.