Dave, thanks for the tips, you're probably right that this will be a bigger job than I think (it usually ends up that way
) However, I think this rust was caused by hidden body damage, not by general rusting conditions, although I have heard that the W210s often have rust problems. The rusty metal in the wheel well appears a bit misshapen in places, making me think that a rock or something must have kicked up from the wheel, doing damage that went unnoticed for several years. I inspected all the other wheel wells and they are rust free and in perfect condition. My hope (wish?) is that this is an isolated event, not an indication of things to come. I guess I'll find out eventually, one way or the other.