[morzh]

Yesterday I decided to investigate the issue of the crackles while tuning. To remind, it only showed on BC band and only between 1200 to 1600 kHz.

I took the tuning cap out and gave it a good bubble bath with soft long brush between the vanes, then dried with heat gun on low.
Then left overnight and today I connected it to a doubling rectifier via resistor 30K.
I put the voltmeter across the plates and turned it on. I did all three sections one by one while turning the rotor.
No sparks or jumping voltmeter value, meaning no shorts and no burning debris.
I also didn't expect the crackles to be the result of the bad wipers contact to the rotor as there are 4 of them - no chance of such repeatability.

So....put it back, turned it on......no crackles anymore.
Put the dial back, then the pointer....same, no more crackles.
I will have to realign the bands.

Mystery.