Fuel pump issuse

I have a 2006 mazda demio 1.3L, and it had the fuel pump replaced 1y 8m, 2 weeks ago, the car suddenly wouldn't start.

I have taken it to the mechanics who agreed it was somthing with the fuel pump and dropped the tank, he has said it was a lose/corroded connection between the fuel pump and the rest of the sensor assemble thingy.

He cleaned it and stuck it back on.

Car took about half a second longer to crank than normal and seemed to hang at 2750rpm. Before accelerating, it has gotten worse and worse since then, with it now taking about 8 sec to crank.

The fuel pump is still turning on when the car starts, and the mechanic has said that it could be the pump itself, but he doesnt think its related to the connector becuse "either the pump works or it doesnt", he believes it to be the pressure relief value due to having the injectors open for longer making it run better

So my questions are pretty much

1: Is it worth splicing and soldering that connecter that he "fixed" as this wasn't a problem before he was in there.

2: Can it be the value and / or other parts of the assembly

3: If there is something else in that assembly, can the assembly be taken apart to replace it as a new one is gonna be in the thousands

Im really starting to lose faith in my mechanic and definitely cant afford to keep this up as this fuel problem has already ate up 600, and 570 last time, and probably another 700-2600 if i cant fix it.