I got a spare edge connector from some nice Italian guy and I soldered it in. It works perfectly!
I also bought a replacement MFM harddisk via someone at A1k.org. I got it to work after many tries by circumventing bad sectors on the Amiga partition. As the MS-DOS-partition avoids these automaticaly, the Amiga apperently does not. So I chose the cylinders that are not bad for the Amiga side. The partition is quite small, but it works well now.