pretty easy to spot since its visible under the hood, but
there is a factory installed sound deadening material adhered
to the top of the fenders that can cover up rust areas.
Pay attention to the seam just inside the edge where the
hood meets the fender. E9 fenders are welded on, which translates
into beautiful lines but a potential rust breading ground.
The photos below show this area in detail.
problems in the upper fender area is attributed to moisture
from both sides, top and bottom. Rain water can settle under
the hood and find its way into welds and cracks, and the
road wheels throw water into the seams from underneath.
The common theme you'll hear among coupe owners is, "Don't
drive in the rain!".