Vintage Synth Repair

hey guys...

i come to you with a slightly off topic problem. i'm guessing it
involves capacitors or something like that, and it might be a problem
someone could have with a synth, plus you guys are a wealth of
knowledge  sooo....

i'm having a problem with my fender bassman tube amp. it's spitting
out noise randomly. sometimes it doesn't do it at all and other time
it gurgles and spits out random volumes of static noise. i noticed
that if  i gave it a sharp nudge it'd go away for a second. same as if
i turned it off and on. a friend of mine had the same thing happen
with his off brand tube amp. i'm guessing all the components are
original so there are probably some components that are 40 years old.

am i right about needing to replace caps? if so, should i just do them
all, or can i test for good and bad caps?

thanks again for all your past help guys,
johnny