Tube preamp reliability vs SS?

I am considering buying a Conrad Johnson classic 2se pre or a used McCormack LD-2 preamp. 

 I have never used a tube pre, and am curious as to the reliability of the tube, I like to be able to turn it on, maybe wait 30 min for warm up before jamming tunes.  This is fine, my concern is the reliability of the tube, how long will it last?, also, is it a pain to change when it goes bad? Can I change myself, or must I send to factory just for this small tube? 

• Would the the action of me putting in the new tube void any warranty, not that 3 years is long anyway  when it comes to warranties.