Hi Arie, this is my first post on this thread. Congratulations on a great machine. I haven't read all the posts but I am surprised you stayed with the router spindle for so long. My understanding is that the bearing arrangement in such spindles is not really up to high precision work. I have three and all, even the 400 EUR one, have only a single deep groove bearing, with no preload, at the business end. Have you found your router spindle to be up to the rest of the machine or did you solve the bearing issue in some other way. My interest is that I intend to add a high speed spindle to my machine but I'm not sure the router route is worth the effort.
I see you have made mods to the mount and are considering an upgrade so I guess you are not entirely happy.
Best Regards
Phil
PS: Two of the three routers I have have the same run out issue you found on yours. The runout on the expensive one is not detectable with a 0.01mm DTI.