Following up on my original question regarding underbody corrosion.
Take a look at the video below, created by Redish Motorsport, BMW M specialists in Bristol UK. Redish have been doing fantastic underside restorations on E46 M3s for years, including reinforcement plates to cure the floor cracking problems, which are a result of too thin steel, poor quality welding and bad design (putting spot welds in high stress areas).
Their attention to detail is becoming legendary.
I had already contacted them about getting the rear sub-frame restored on my car (at 38k miles the sub-frame is covered in significant and unsightly surface corrosion) and powder coated, and they said they were about to do a sub-frame removal job with another customer's car, for the first time, to facilitate underbody refresh.
The video makes very depressing viewing. It starts reasonably well, but gradually gets worse and worse, as they examine the underbody surface in detail. The rust is all over the place, in the sub-frame area, and at the bottom trailing edge of both cills, around the boot floor aperture, inside the fuel filler tube, and and and.....
It looks like BMW now either use very poor quality steel, or their pre-paint preparation is very poor, as this car (2011, and 100k miles, but obviously very well cared for) has rust growing all over the underfloor panel adjacent to the rear subframe and everywhere that has not been protected with seam sealer.
And this rust is growing
underneath the electro-coat and the painted surface, so not caused by stone chippings on the surface.
I am pretty shocked at the lack of protection. BMW are getting away with it, because the multitude of under-floor plastic panels, cill covers etc, hide the actual problem.
A 12 year anti-corrosion warranty with more get outs than I can shake a stick at, is not going to provide me with much comfort.
I had intended to keep my E92 M3 indefinitely, but this is making me think again. Probably £2.5 to £4k to have the Redish job done, and doing it will almost certainly give BMW another reason to avoid paying against any corrosion claims in future, on any part of the car.