Please forgive me if I get the SP 1408 and the SP 1411 fittings reversed

(It's been ~ a year since I've seen the "old school" ones (which I'm referring to as the 1411).
I don't see the wall deterioration in the pics :? I
DO see a missing, or deteriorated gasket behind the liner!
The SP 14XX goes in from the front of the panel and needs no gasket where it penetrates the pool wall (the liner and the black gasket keep the water from getting in there

)
Unless they drilled the hole for the return fitting, there should be a notch for the new one to fit into correctly, with the screw holes lined up properly
If the wall is deteriorated so much that you can't get a new fitting in, let me know and I'll tell you how to patch it and cut in a new return :-D
As said, from the pics, it looks like the entire inlet fitting is shot

and you need to replace it - which will require access to the back side of the panel.
Can you try putting a magnet on the wall just under the fitting to see if you do, indeed, have a steel walled pool? If you have steel, you can patch that and hole drill another opening in it to accept a new fitting
For right now, the water is down enough in the pool to make any repair (we just have to figure out what you need to do

) - I'm more than willing to 'walk' you through this - I just need to know exactly what we're dealing with