[Arran]

 There are two common modes of failure with the mica caps inside those mini IF cans, sometimes made by K-tran but not always. First is the silver migration problem, where the silver spray starts to migrate towards that brass rivet in the center and cause leakage. Second is that the actual connection between the silver on each side of the sheet and the legs on the IF can become open or intermittent.
  I highly recommend ruling everything else out first ahead of the IF cans if you are getting crashes of static, starting with dirty tube sockets, followed by faulty paper caps, resistors, and solder joints. Opening up one of those IF cans and taking the micas out of it is a PITA. If you want to learn about replacing them then you are in luck, shango066 on You Tube has just started a series repairing a radio with this problem, though it's on the FM side.
Regards
Arran