Originally Posted by RMB
Here are a couple pics of the underside of the seats. Might not be anything but I wanted to throw this out there. Any thoughts?
Throughout this thread, I think we might be looking at two types of chemical residues. I'll refer to them as Type A
and Type B.
Type A : the yellowish residue shown in your E90-M3 photos (Post #85, page 3) is almost identical to what I found on the underside of my car's seats (F30-335i mid-October production). I believe this may well be a chemical residue left over from the galvanic production process, when the seat frames were supported by trays on the assembly line. You will note the mostly linear shape to the residue areas shown in your photos.
My dealer's service manager examined my seats today, and he agreed with my thoughts. He mentioned that he had already observed about 10 F30s with genuine signs of brownish-orange rust, both on the underside of the seat frames and on some of the seat hinges (see Type B below). My car's seat hinges are painted black; apparently, hinges in the early production cars were not painted. The cars with rust referred to by my service manager were from earlier production.
Type B : presented by the OP, Steve_Jr, (Post #1), where large, amorphous and random areas of brownish-orange oxidation, being typical of surface rust, were evident in the photos. If my seats presented Type B oxidation, I would most certainly request a replacement seat frame under warranty.
But I would caution anyone with the Type A residue to requesting a seat dis-assembly and frame replacement, if in fact BMW would even authorize such a claim. The potential cure may be worse than the apparently harmless cosmetic change to the underside of the seat frame. If a seat is dis-assembled, it will not likely be re-assembled in exactly the same way as it was originally at the factory. There are bound to be minor variations in the padding after re-assembly, in addition to potential rattles and squeaks that were not previously present.