As suggested by Phil i have injected silicon grease into the Centa unit, easy to get all the way in using a large syringe with a small tube.
Been out for an essential journey and the result is a noticeably smoother ride with less vibration felt through the seat. Surprised that a bit of grease could have that effect, wonder how often it will need doing though.
Still got the annoying rattle and knocking sound at around 3.5k rpm though that i would like to get to the bottom of but try to ignore!
Glad to hear that it has worked for you, this is the first feedback from a machine with the standard set up. I believe the friction between the rotors and the rubbers causes some shear forces in place of purely compressive ones. Every couple of thousand miles or so seems a good interval but you will notice when it needs a bit more.
The rattle/knock at 3,500 is probably the NVH kit allowing the bevel box nose to jump up and down ( if you have the NVH kit of course).
