Take the cap off. Spit on your finger and wipe off where the cap goes. If it bubbles up there is your leak. No bubbles no leaking valve core.
As a teen working in a filling station we always did this when repairing leaking tires and tubes.
I thought the 36 Chevrolet was the last one with knees.
Mine rolled of the grease rack and out into the street. The only damage was the rear bumper bolts sheared off and the knee front end was about 2” lower. It still drove fine.
I have them. They work as advertised. Big improvement over the earlier led bulbs that replaced the incandescents. Being focused you don’t need the polished reflectors. Your rusty reflectors work fine with them.