I have the same one and the brass valve does push down and seals. When water does gather in the trap I turn off the air feed and using a piece of wood to push the valve up and it dumps the water out.
Well I did a spoiler with similar damage on the edge as yours and just put two coats of 2k high build, mixed primer, hardener but no thinners. It seems to have filled in the feathered edges now I've covered it with a dark blue clear of base.
I only did the repairs with a da before primer to feather the edges back with 180 grit. Then when the primer was dry block flatted with 800 wet. Cause the rest of paintwork was good I used a grey scotchbrite pad and Farecla g-mat. Then when top coat was dry wet flatted with 2000 by hand with...