If it was affecting the VCO then FM wouldn't lock. Up North here we
get this problem every so often. It's a cap on the power supply,
usually somewhere around the driver or pre-driver. Just get a can of
freon from Radio Shaft (if they still sell it) and squirt the caps one
by one until you find the bad one and replace it.

But how does this work, I mean how one could see whether the cap is
defective by spraying it with freon?. Is just squirting the caps one
by one, while the TRX is warm, and see which cold cap creates
distorsion, or the defective cap will show up in some different way?

Thanks,
Julian