I have a 1989 944 Cab, It is very difficult to refill at the browser. Any ideas?

 

Have you done any basic troubleshooting? There is a round spring loaded flap generically on all cars. Test it out with your finger or a short rod and make sure it moves out of the way correctly. Push the flap aside and shine a flashlight in there. Make sure there isn't some foreign object jammed below the flap. It is a favorite place for hiding children's small rubber toys! I would suggest you get a length of rubber or vinyl tubing about the same size as the filler nozzle on your fuel pumps (you use the term bowser, I assume you are in Europe) and make sure you can get about a foot of hose into the opening without meeting any obstruction.

I've had the fuel filler on my 85 car fully disassembled and there is quite a bit of infrastructure involved to keep fuel vapors from going straight to the atmosphere. But even if the vent lines were totally blocked, air is so compressible that I would not imagine that could discourage the fuel from entering the tank. The metal filler tube itself has an internal tube that the fuel goes through and an external tube around that with a variety of holes and passage ways to allow fuel to stay in the system and not run out on the ground.

Not your problem but an anecdote. I was driving a diesel Jetta and stopped for fuel. The fuel nozzle would not go into the opening. Looking in, there were small tangs extending into the opening that blocked the nozzle. I called VW roadside assistance and they said go to another station. I thought they were nuts but sure enough, at the next station everything worked perfectly. It seems the tangs are actually points in an electrical circuit. If the nozzle is not the proper size for diesel, the circuit is not completed and the tangs are locked out. Theoretically keeps you from misfueling the car. The first station had old fueling equipment with the incorrect size nozzle.