I own 2 E30's from 1988, and they both are/were very rusty, considering the general condition. So seeing your 1988 M3 just conferms my suspicion that BMW had a problem with their bodycoating this year.
I also own and two 1986 models and they are very rustfree.
Why is there not enough time to do it right, but allways enough time to fix the errors - I borrowed that, just so reallistic in my line of work.
Not allot of progress so far but.....we got ourselfs a lift. Brand new and awaiting to be hooked up to some power. Now at least we can do much more work easier. Just need to finish sandblasting now....