Scenic RX4 vibrations

My RX4 is giving me (more) gray hair ;) It feels I have almost changed every part of it the last years. For ex, gearbox, prop shaft(Dave Mac Prop), coil springs, cat, fuel injectors, clutch, final drive sealings and not to mention several new prop shaft bearings.

Now since a few months there is a severe vibration with the prop shaft mounted. If I remove the prop shaft the vibrations go away. Now that might seem to be simple, the prop shaft is to blame, but there are number of confusing things:

1/
With the car lifted the prop shaft does not look "unbalanced" when rotating.

2/
The prop shaft joints and bearings are ok.

3/
As far as I can tell the rubber damping disc(hardy) is ok, also the metallic ring damper's rubber does not seem too bad.

4/
The vibrations are also there with the old Renault original prop shaft (+the sound from the bad rear bearing), though maybe a little less notable.

5/
The vibrations are there with both summer and winter tyres.

6/
The viscous coupling seems ok. If I jack up one rear wheel(with the prop shaft mounted) I am able to rotate the wheel by hand force.

The final drive gets around 35-45C degrees warm after driving 15 km with the prop shaft mounted. Without it is around 25C. Does that seem ok?

I feel stuck as what to try as next step in "debugging" this! I could send the prop shaft to Dave Mac for checking, but it is a bit "costy" and since the mentioned things are not clearly pointing in that direction I would rather not chancing without be more convinced about the prop shaft being to blame.

Due to the car's many faults it has periodically not been in use and a strange thing is that, if I remember correctly, the vibrations started after the 3-4 months in the beginning of the year when I did not use it. Another strange thing is that during that time the final drive's prop shaft/viscous coupling sealing started to leak so much that the final drive became more or less without oil. I fixed the sealings before I started to use the car again, so the final drive were never driven without oil.

Could it be possible that I messed something up when I changed the sealings if the final drive?

Any other suggestions? ;)

Scenic RX4 vibrations