ProV1, did it happen w/ your E420? If not, I think it's because the previous owner of your E55 did not maintain the car well enough.

There is no rust on any of my MB.... even my 2001 E55. This could be because I live in CA and the car has always been in CA... but it could also be because I regularly wash my car. If I drove it in the rain, I always washed it the first day the sun came out. In every wash, I power wash the under carriage to minimize sand and other debris left.... and I always wipe clean the door, trunk lid, hood, gas compartment and all the gaps in between....

Having lived in Mid West before, I certainly avoid Mid West cars. But there are people like me in Mid West who washed my cars in a heated self-service car wash during the winter.

BTW, what kind of problems do you have w/ your E55? Mine was only MAF and instrument cluster.

 

Knocking on wood...Maybe it's luck but I haven't had any major problems either with my MB's. Like zoink mentioned the cluster display on my E55 and then nothing major on my prev. E420 and I sold it at 140k miles. It ran better than any of my newer cars and no rust! Again, CA cars, especially those not near the ocean, maintain the cleanest undercarriages and hardly any rust if any...