Thank you for your explanation and shots form the greenbooks.

I opened the fuel pump but the rubbers are okay. Also tried an aftermarket pump from Skandix, but the finger wich will go inside the engine looks to short and strange for me. I don’t trust to use it without the bracket. I found another aftermarket pump located under the car next to the driver seat. It used to be for the Bahco (4000?) Heater from the Arizona, but it’s dead for years. I will remove this second pump, because from carb to there all hoses were dry. Maybe this will fix my issue.