If the car has a full service history, stamped and accounted for, then it doesn't matter how many owners it's had - MB should honour any corrosion repairs under the 30 year Mobilo Life warranty.
You really do need to read the small print of this however - I have a feeling that if there's any (un)reasonable excuse for them not to repair it FOC, they'll use it. Hopefully this behaviour is changing now we're getting away from the Daimler-Chrysler years.
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Current metal:
2002 (C215) CL500 (Batmobile), Obsidian Black, 54k miles
1997 (C140) CL500 (Bismarck), Emerald Black, 134k miles
1991 (W201) 190E 2.6 Sportline (Blake), Almandine Red, 133k miles
1990 (C126) 420 SEC (Bruce), Astral Silver, 111k miles
1978 (R107) 350 SL (Boabby), Signal Red w/ silver hardtop, 115k miles
i have a 2000 cl500 and found some corrosion to the inside of the rear arches as they are made of aluminium it was the horrible white dusty stuff cleaned off the paint masked it off and undersealed both sides looks ok with no more risk of water creeping under the paint i would say this mod is a must to stop the problem creeping around the rear quarter.
I HAVE A CL500 BLACK...AND THERE IS SOME BUBBLES ON THE ROOF BY THE RUNROOF..NO RUST YET BUT IM SURE IT WILL COME.... BUT THEN AGAIN I LIVE IN FL WHERE IT RAINS A LOT AND THEN SUN LOVES TO SUCK THE BLOOD OUT OF YOUR PAINT