Re: 03 VW GOLF TDI - Cutting out the second it hits reserve and diesel light comes on
It could be a lot of things including sludge in the fuel tank momentarily blocking the pipe from the tank. Retail outlets in the UK have published apologies and offered to pay for repairs to cars damaged because of silicone contaminated fuel.
If you are happy that the changes you made have not resulted in any air-locks, it may be that the sender isn't working on the fuel reserve / expansion tank, which I think holds 5 or 6 litres.
Next time you fill the car, when the garage fuel pump cuts out, press the little valve that sits at the top of the fuel filler neck on the car with the metal end of the pump. You should hear a hiss as trapped air escapes and you will be able to fit more diesel in the tank. Continue until you have the tank full, being careful not to spill any.
See what happens the next time the the fuel warning light comes on.
If there is no change, then maybe get your mechanic to drop the fuel tank and clean it out.