Photo above shows the "anti-blow-out" clip used on original MGA 1600 type side curtains. These can be retrofit to other frames with sliding rear panel. Not sure if they will fit on original 1500 type units with the flip up bottom panel. Photo at right shows the clip installed on an aftermarket double slider side curtain, just a bit higher than the original position.

These clips are available from Clarke Spares and Restorations. Use the standard slip fit plastic sleeves (separate item) to prevent marring of the chrome. Use a bit of finesse when closing the door to get proper alignment. Open slider window may reduce pop-out effect on final closure.