hmm if it is the returen line I can;t see why it would cause your problem.

On the bright side you have opened up a very problematic area for these cars. Yes rust forms there at holes develop (I did mine...). You are openeing up the assembly, in there you will find the fuel pre-pump. It is responsible for a high volume low pressure siphoning of the fuel up out of the tank to the main pump for pressurizing it... This pump always needs changing after a few years. You should see if your works ASAP before ordering the sender. Don;t worry it is cheap, around 35$ I think. At the same time again you will find the small hose that goes from pre-pump to sending unit tube. This hose always needs changing after a dozed years, it deteriorates and falls apart, hence no pre-pump sucking and hard starting and poor drivability, mainly with less than half tank gas.

I seriously suggest you buy all the following:

sending unit
pre-pump
small fuel hose (sometimes incl with pre-pump)
pre-pump sock (2$ filter)
sending unit lock ring (cheap - the old one is rusted and bent)

on the hoses to the sending unit, cut off 1/2 inch and slide into the new unit, clamp with new clamps. Some vaseline helps sliding and help seal.

You can hear a buzz if the pump is working. The car still usually runs without it, but with problems. Hell that might even fix your problem. check fuse and also measure the wire going to it for +12V when car is running.

Hope this helps. Don't feel overwhelmed, I broke the wires off the top of mine and took the opportunity to do all the above. See it as an opportunity. It is part of the maintance of these cars every so often anyway.

IMPORTANT: When knocking the lock ring around (slowly and take your time to not damage the tank) keep in mind that it is steel. If you use a steel screwdriver it can spark, hence KABOOOM! They suggest a brass punch. Hell I used a regular screwdriver and said a prayer beforehand. Just make sure you are well ventilated and avoid scratching/sparking. It took me approx 1 hour of tapping to get the thing off, but i was very happy to find a CLEAN tank and cleaned everything off. Vaccum up the shit on top of the ring constantly so it does not fall in the tank.

Be clean, but most of all be safe.

Ciao,
Greg Mustang
Ottawa-Montreal
Canada