Anyone Blow a Release Valve on Power Caps?

I went to turn on my Sierra Denali power amp yesterday and noticed it was wet on top plus there were dried residue spots everywhere. I dried it off (a bit oily) and opened up the case. It was even worse on the inside. I dried things up a bit and did a visual inspection. The Denali has four "beer can" sized 63v 82,000 mF power capacitors surrounding a 2.2 kva transformer. All four of the caps have a small gray plug on top of them. One of the plugs was extended above the cap with a clean hole in it. Obviously, the liquid was the electrolytic fluid inside the cap and it had blown out through the hole. I called the folks at Sierra and they will take care of it and even upgrade a few things for me. Nobody there had ever seen that happen before. We had not been playing music at a loud volume. Each of my two Denali amps is on a separate dedicated 20 amp circuit. The amps sounded fantastic the previous night (my wife even commented on it). My wife only noticed it before turning the amp on, so she decided not to turn it on. It may have happened just after the amp turned off the previous night. I can't imagine it happened while we were listening to the music -- wouldn't it have been noticeable?

Has this happened to anyone else? What might have caused this? Can I avoid this from happening in the future? If this is just a case of a bad cap, there's not much I can do, but... Thanks in advance for your help. I did upgrade my XLR cables from the preamp to the amp a week ago, but I can't see how that would damage anything. Help!