I did upgrade to an Avalon Linear mount. Coming from an ES EXOS2-PMC mount this is a big step, at least my expectations are high.
The new mount sits now on top of a rock-solid Celestron tripod.
Changing the mount required a new Losmandy prism rail for the OTA and this allowed me to do outstanding improvements of how the guide scope is attached and how cables are handled in general. The guide scope is now attached to a prism rail on the top of the OTA with two tube rings at two distinct places, which hopefully minimizes flexure. I attached a metal plate from the hardware store to the prism rail on top of the OTA and attached the USB hub, which I am using as a 5V power distributor to it with some zip ties, the other USB hub for data is similarly attached on the opposite side. The 5V power is required for the dew heaters. So far they worked for me even in cold temperatures as low as -10°C. The intention was to use one powered USB hub with USB sockets for 5V power supply and sockets for data transfer. I bought such a USB hub  but it turned out that I often had data connection problems, so I use a separate USB hub for data now, which eliminated the problem at the cost of a 2nd USB hub, but a non-powered one.
I had quite some hassle with the power supply for the mount, since the dc-connector of the power supply did not fit tightly into the dc-socket of the Avalon Linear mount. The connector is a 5.5-2.1mm DC connector but despite the fact that this is the correct dimension as specified for the mount it did not sit tightly in the socket. I have pried up the little spring metal that is inside the socket so that it presses towards the inserted connector and additionally I do secure the connector cable with some cable clip and that seems to do the trick.
The stack of metal washers that can be seen on the side of the OTA is for balancing the OTA in the 3rd axis, basically it counter balances the EAF.

So for the time being this is it. I'm curious how this new setup and the Avalon Linear will help to improve the quality of my images. Reliability is what I am aiming for, I hope to have achieved a more consistent behaviour of the gear and thus overall better quality.

As always: comments welcome

CS
Gernot