[GrimJosef]

If I remember correctly there was a failure mode associated with the main electrolytics oozing liquid under thermal cycling and the liquid then dripping onto the pcb and corroding it. The solution (no pun intended) was to invert the capacitors. That generally stopped the oozing, and even if it did occur the liquid would tend to sit as a droplet on top of the capacitor where it did relatively little harm. I don't remember at what stage Quad discovered this fix though. I recall seeing 303s with the original factory-fitted capacitors already in the 'upside-down' orientation.

Cheers,

GJ