Hi and welcome to JustAnswer,
Thank you for the question and your patience. Should you still need assistance for information purposes only...
Initially, how was the cleaning done please? ...was spray/chemicals used something like DeoxIT DN5 or LPS 03116 Contact Cleaner or equivalent?
Still, proposed preliminary try (if have not been done) spray with compressed air the insides of the "...front panel main tuning..."
A friendly reminder: Voltage measurements by its very nature requires that the unit be plugged in and therefore LIVE! Please exercise due care and caution.