In car boot sales, I got a very used and scratchy Tivoli Audio Model One, so only by turning the dial was the scratchy tuning problem completely solved, and the radio worked again. That confirms that the problem is not in a variable condenser and should not be changed (as 60 years ago, radios had the same variable condensers and are still working perfectly). Maybe the dust comes into the condenser, and because its structure is tighter than the one in old radios, you need to clean it up (perhaps by turning it), and that's all. So I confirm that just a simple turning for a few minutes works perfectly.