Thank you for that info E_T_V!The fuel delivery valves are outside of the pump so can be changed in situ I think. Probably best swapping them from a second hand pump as I've virtually never heard of them fail.
So I'll probably can solve this without removing the pump from the car. That makes it quite easier, I think.
Do you know if I can buy new valves? Do you know if Bosch sells them individually?
I'm going to google it but I'm also going to search for a second hand pump.
Thank you once again for your ideas and tips.