tried out my old amp again and found that adjusting the volumes and high/mid/low causes a little crackling. My guitar does the same with the volume and tone knobs. The guitar is an ibanez EX140 from 1990, the amp has to be around the same age. Is there anything I can do to fix that?

also, I really like the chorus and reverb on the old amp (crate G40 CXL), much nicer than the DSP effects on my main amp (crate GFX212). Is it worth gutting that and trying to work out something with the electronics? I think i'm going to sell the 212 and get something quieter and either sell or gut the G40.
On the knobs, its just some dirt in the pots. Get some pot cleaner to fix that. Its not a big deal at all, and if its an old amp I wouldn't be surprised.

Before you gut it, I'd check and make sure that Crate doesn't make it as an effect (I dont think they do, but it's still worth checking before you put your amp under the knife.)
thanks. i could probably just get another chorus pedal. nothing really special about that one except its free and could be a fun project.