External cam QR's work okay actually - but are often of alloy construction for the lever, nut and facings - the serrations wear away quite easily. When used with horizontal dropouts - they suck period. They're really intended for modern day vertical dropouts.

So if you have horizontal dropouts - switch to classic steel quick releases - Shimano, Quando, etc...

Also, one more thing. When you had the wheel trued, did you have the wheel dished properly? Because if the wheel was off-dished to the left side, then you have been forcing the wheel to the right to center it while clamping down the quick release. The wheel under load will naturally want to settle back into the parallel plane of the dropouts resulting in the wheel moving left and closer to the non-drive chain stay.

So check the dish of the wheel while you are at it...


=8-)