[Arran]

It could be the IF cans but before playing with those try giving the volume control and the tube sockets a good cleaning, it could also be a cold solder joint so it worth checking your work there. I am suggesting all of these first because breaking into an IF can and removing and replacing the capacitors/condensers inside is finicky work that should only be undertaken as a last resort. If they do turn out to be the culprit try to measure the exact size of the originals before diving in as they are not all the same size. I have replaced the capacitors inside an IF can just recently and contrary to popular belief they are not all 100 picofarads (micromicrofarads) , and you do not have to used silver micas as replacements, precision ceramics capacitors work just fine and are maybe 1/3 the cost of silver micas and are smaller.
Regards
Arran