I lost my first left hand panel in 1976 at a road race meeting at Mallory Park in England. It was stolen when my bike was parked. I know it was stolen as the knob was left on the ground by the side of the bike. Ever since I have put a rubber washer between the top of the cover and the underside of the frame tab. I have then replaced the knob with an Allen screw with a washer under it. The washer needs filing down on one side so I use a stainless washer and so no rusty washer. I always carry the correct Allen key with me. HTH
Just a quick refresh of my thread. Still on the hunt, thanks to the guys who have suggested why the LH side panel was missing when I bought the bike. Makes perfect sense to me, but is a touch disheartening as it looks like I'm looking for the proverbial hens teeth. That said, I'm a glass half full person, so hopefully this refresh of the thread will bring some good news? All the best and stay safe.