Heat distress like that is always a good reason to reach for the ESR meter ... Seriously though, as soon as you can afford it, invest in one. The "Blue" is very reasonably priced, and is a fine performer. You'll never regret a day of owning it. The thing that makes an ESR meter different from the static DC tests that you are carrying out at the moment, is that it applies high frequency AC to the cap, which is what is required to arrive at a true ESR value. It is this use of low voltage AC, which also makes the meter able to perform its test with the component still in-circuit, which is a huge advantage, particularly when a board is hard to get out of equipment. This assumes of course, that you can get to the cap's leadouts on the top side of the board.
Arfa