i have a mcintosh mc602 power amp which i bought in 2012 from audio classics. i only use it like once a week. it sounds fine to me. should i worry about maintenance on this unit? 
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As long as you've been using it, and it's performing well, it should be fine. If humidity is an unaddressed issue, you might want to check it for corrosion inside. Using it is the best maintenance. 
i live in los angeles california. i guess 'humidity' is not an issue here. am i correct?

Probably not. Smog maybe?
i read that smog here in l.a. is bad but during the 50's and 60's when you would breathe, the smog was so bad that your throat would hurt. not today but i know where your're coming from!! LOL!!
Just use the amp, it’s built like a tank.