2011 cxu mp8 7th injector

I have air bubbles in my diesel tank. I know it is likely that my injectors have gone bad after 100k miles because well Macks apparently suck for injectors.

I did read on another posting from a few years ago that it can also be caused by some air valve by the 7th injector. Google searches bring me nothing to relevant unless the valve they were talking about is on the opposite side of the engine (driver's side). I don't have codes but I can't expect one considering the 7th injector is just for letting looks at this point.

I do have hard starting issues which started as an overnight problem but now have suddenly gotten much worse and cause problems immediately after shutdown almost. I was told by a shop that my davco, fuel filter housing, and injectors are all bad/leaking. I could almost believe 2 out of 3 especially with how much I've been pumping on the primer for a while now, but it sounded enough like covering their arse to warrant some more googling. The starting problems got worse today and I did notice a slight miss for a few minutes which is gone now but my oil pressure is now idling around 30 which is about 8-10 psi lower than normal for me I think, haven't driven it much in a year.

The shop did run clear lines to see the air was coming from the front of the motor.

Please take into consideration I don't know a lot. I've had the truck for a few years but didn't have anyone to learn from and have only picked up what I had to as I go. Thanks in advance for any advice