should I buy this tube amp?

There is a Unison research simply 845 for sale at a crazy good price, but it has been in storage for the last 2 years. It was hardly used after purchase and has been in temperature controlled storage since. The amp works but there is a distinct hum from the transformer and crackling/ popping sound from one of the channels. Switching the tubes from left to right will change the crackling sound to the other side as well. I assume changing out the tubes will take care of the problem. Other  Questions: 

Does prolonged storage (2-4 years) cause any kind of damage to capacitors? Perhaps cause them to dry out? 
Can any other components be affected by prolonged storage? 
what other important information do I need to ask about a tube amp prior to purchase?