Panasonic Viera screen flicker cycle

I FAILED TO FIX our 13 year old 42 inch Viela TH-L42E5 (sold in Japan), the image of which moves up and down by about 5mm or so every second or so.
I tried everything in a Youtube video
Remove plug and press power for 30 seconds
Plug into a wall not a multi-socket adapter.
Replace HDMI cable
Push in HDMI cables and socket
Reset settings
Attempted to turn off Ambient Light brightness adjustment (none)
Attempted to change the display mode to sport (none)
Tried different zoom settings (normal, zoom)

None of these worked, so
I removed the screws on the back panel of 4 types, about 30 or 40 screws
Removed the rear panel and used a can of compressed air to blow away the dust, of which there was quite a lot, that had formed on top the central LED driver (?) panel - the brown square in the image below. I also blew on the other panels.

But the image still moves up and down every second or so. The frequency of the movement MAY have decreased but I could so more dust to blow away. The flicker is not that bad (yet) so we will take our time about getting a new television. I think that 13 years of service (bought and built in 2012 in Malaysia, now 2025) is okay so we may get another Panasonic.