Polishing plexiglass windshield

The plexi windshield on my Mustang is likely original. It's structurally fine but has gotten cloudy.

Over the summer I polished it several times with Meguiar's PlastX. This brought it back to an acceptable level of clarity, but after sitting for a few weeks (either in the sun or under a cover) the windshield would cloud up again. Another round of polish would bring it back to serviceable.

Any suggestions on a polish or sealant that will keep it clear? At the moment I can't see through it at all if driving toward the sun. I could order a new windshield from UPD but I'd rather not spend the money. I'm tempted to spray it with a UV-stable automotive clear coat. I've done this on headlights after wet sanding and it works to keep them clear for years.

Just by hand. I'll try the buffer before I shrink wrap the boat for the winter. Even by hand I could see the oxidized layer coming off on the wax pad.