Sorry to hear of your problems with springs. On the reverse side of the coin, I've just had the rear shocks & springs replaced on my 1989 W201. Not because they were problematic, just because the car has covered 196k miles and I figured they might be getting tired - plus road surfaces have deteriorated markedly of late. Got the old components back from my indie and the springs have never been replaced before, as they still bore the original date stamp (3/89). Other than some minor surface rust, they were in very good condition. I give the springs a light coat of waxoyl annually, so I'm sure that contributed to their longevity.
That said, I had a 1993 W201 that had two broken rear springs at 60k miles.....so who knows?