To be honest, I completely forgot about that other thread. My apologies. I fear this is another symptom of advancing age. I had given up on the UHF for the time being, then bought a new receiver that includes UHF which put it back in my mind again and I decided to look for a solution. I forgot that I had already done this. My brain plays tricks on me from time to time.
To get to your point, I have carefully checked the antenna for movement in relation to reception quality and have never been able to find the slightest connection. There is no observable movement at all except in very strong winds, and even then only very little. Reception quality sometimes is perfect even when strong winds are blowing and sometimes crap when it is completely windless. I can't find any connection there. Also, reception was excellent for many years when I also had no guy wires or other support. Naturally I can't rule anything out completely, but antenna movement just doesn't seem to be the issue.