Pictures please.
The colour, dimensions, style etc. are all good clues when identifying trimmer capacitors.
However, a common problem on older trimmers is dirty contacts, the wiper that contacts the moving plate tarnishes (I spent many hours stripping down, cleaning, re-tensioning these contacts as a trainee TV repair tech) so a squirt with a good quality contact cleaner followed by a clean up might just sort the problem for a few years.