Thanks for your answers.
Don, the shaking was difficult to identify as it was not present all the time and not every night (it just shake for 4 or 5 sec then it's ok for 30s). It's just that some nights autoguiding was crazy and some other nights ok. I thought it was something to do with the balance, the encoders, PXP model, Scitech param...
Remove the old grease and put new one is on the planning now.
I will test probably tomorrow night, first to see if the shaking is still there and with different encoder mode. I will see what tics/rev we have in our Scitech param.
I am still surprised that grease can have such a high impact on the mount and blocking the motors (tightness of the worm on the gear was not touched for years)
Dan, ok I will look and let you know about the position error we have
Jan, thank you for these info. So it means we have a circonference of 628.32mm and at 50nm per ticks we obtain 12.5 millions ticks per rev, right?