[MBZ] 1999 E320 rusted front spring mount?

[John Monocello]

I'm new to the list and am hoping someone has experience with this. I have a
1999 E320. It was raised in Texas, but spent last winter in Michigan. I was
getting it ready for winter and noticed that half of the front drivers side
top spring mount has rusted away where it meets the frame. I find this
puzzling because the car has not seen salted roads until last year and I'm
pretty thorough about maintenance and washing the undercarriage. The
passenger side looks fine.This is not what I expected from a $40k car.
Anyone know if this is a common problem?
 John Monocello