Shipping damage...what would cause capacitors to leak?


I sent a NuPrime ST-10 via UPS Ground from San Diego to the San Francisco Bay Area and the buyer found that there was black goo leaking out from the back of the chassis.  Upon opening the amplifier he found that two of the capacitors were leaking.  Being of a non-technical nature, I'm wondering what might cause something like this to happen?  Could it be from impact?  Or maybe the package was left in a truck in high temperatures?  I sent just before July 4, so the package was probably sitting outside in a truck for the holiday.
wcheng2
It's conceivable that if it sat in a truck in this heat wave we're having for a day or two, yes, it could be the factor. My apartment, on the 2nd floor and without the A/C on, can hit 140º so if sat in a sealed metal truck....

All the best,
Nonoise
With the record heat recorded in California right now I am sure that will be the cause.
Anything over a sustained 140 degrees and you are looking at potential issues and by your account this could have been sitting in said conditions for days
Very unfortunate timing it seems
That may not be a capacitor and instead could be melted rubber. Is there any sound dampening material in the chassis? The only sure way to know is for a tech to look at it.

Capacitors can withstand temperatures to 85C or higher. I doubt the temperature in that truck got any higher than what caps experience in a Class A amplifier.