Thank you, M. and Marcus. Good to see a previously unrestored one.
During reassembly I recognised meanwhile it is indeed easier to drop the stone guard through the bucket holes and connect down through the supports for proper alignment, then adjust fender/extension and finally the supports. It seems that many (including myself) first align the fender/extension and tighten them up, creating alignment issues with the stoneguard, which are followed by cracks.
They came to this conclusion as well in this video at the minute 2.00.
Anyway costs me a replacement bucket. Fortunately I found locally two original spares to redo it in the next resto:-)
Wolfgang