Does heat kill tubes?

My system went into a steel container for the past three months while my house was going through remodeling. Container sat on my drive way which receive lots of sun, interior temperature often reached 120+ on hot days. My SF Line 3SE was working flawlessly before packing into the box, it now has a noisy channel which was caused by a bad tube in the buffer section.

Tubes are not as rugged as transistor, but they should be able to withstand 120 degree easily without operation. I assumed if it could survive years of life on the shelf, it should survive a few months in a container. Or am I wrong?