I found that in all the cases of leaky caps, there was so much corrosion that the heat from the iron absolutely would not penetrate the oxidized solder which had turned almost as black as coal, no matter how long I tried (applied heat for close to 30 secs using a solder blob on the tip of a 35W iron touching the cap's exposed SMD legs, board was getting mighty warm but cap still wouldn't budge) and I knew the dangers of turning up the heat further.

I then set about carefully breaking the solder joint through wiggling it back and forth with gradually increasing amplitude - this induces something called metal fatigue in the solder holding the cap down, weakening it and allowing it to pop off by itself eventually with enough rocking.

The key here is never to apply any upward motion - just pure side-by-side rocking.

Granted, that's not foolproof and the pad might still rip due to extreme deterioration from capacitor juice. But with the rocking method, you'll feel the cap "catch" instead of snapping off completely. When that happens, cease all rocking immediately, bring the board to an area with good light (direct sunlight works the best), get a loupe, and delicately work the iron - rednecking a "turret" so the iron is free to rotate about its axis while kept steady - to free the cap from the partially ripped trace. If done correctly, the trace will be left "floating", clean it up like normal, and the leads from the new cap can (very carefully) be soldered back to it. Make a note of the locations of any partially ripped traces so future techs to work on the board will be exercising more care around it and not inadvertently rip it off!

Of course, the only truly "proper" way to carry out this operation would be to commandeer a professional wave soldering station complete with robotic pincers to lift the caps off the board, but meh, little proletariat me can't spare the expense