re: Any HVAC Professionals here? [Updated - Evap Coil Pics pg 4]

Hard to tell from that picture, but looks pretty good for what I see here. I don't see any oil leaks from either. You have a couple options.

Buy a refrigerant leak detector. It will beep when it picks up a leak. This way you can isolate it. You will have to methodically check all areas. If its in the evaporator I would think it would go off when you stick it through the hatch there. They are pretty sensitive.

Insert UV dye into the system then go around and check with a black light flashlight for the leak. This method can get slightly sloppy but it works.

For the amount you are losing every month you should be able to find this leak. Its the ones that only leak 5-6 lbs a year that are hard to locate.

I cannot stress the importance that you need to positively determine the source of the leak before paying someone to swap out a coil, even if the parts were covered under warranty.