[morzh]

I would refrain from changing L2 (antenna coil) for now. It is intact.
I am not sure why, while working, there is a difference of 0.3V between C2 and the grid cap, it supposed to be the same.
When it fails, it is the same, and this is how it should be.

Now, I am not sure what it will tell us, but you could possibly try to see, while the radio is working, where that 0.3V go between the C2 and the grid cap.
Try to measure between them on all 5 pins, that is the C2, 3 taps between the C2 and the Grid cap (all 3 also go to the band switch) and the cap itself. See at what tap it drops from 4.8V to 4.5V. Or maybe it is gradual.
Write it down.

When it craps out, measure the same points again to see, if the drop disapears (all are 2.4V) at all 5 points.


Also. Just for the heck of it.
I think it is the wavetrap (the inductance and trimmer across A to G) shown right at the Antenna strip in the sch.
Disconnect it altogether. It is not needed anyway, and one less variable.