Revox B710 cassette deck spool motor poblem

My Revox B710 cassette deck has developed the following problem: in PLAY, the right spooling motor seems to slip inside the spool which is mounted on its axis, it accelerates uncontrollably, making grinding noise and finally it completely loses friction with the spool, causing the auto stop. The same happens in FAST FORWARD mode which obviously means that the friction between the motor and the spool is very weak. The spool itself is not loose on the axis and appears normally fixed on it.
Has anyone had an inside look in his particular part of B710 transport and what could possibly cause this problem? I'm inclined to dismantle the spool but would need detailed explanation from someone.
Thank you in advance.
 
Thank you for your posts :D, I have found the solution: the spooling assembly is fixed to the spool motor axis by means of a retaining ring with six radial reeds which extend and grip the axis when the assembly is screwed to the axis. Apparently, this steel-to-steel mount doesn't hold anymore causing slipping. Revox have devised a new assembly to replace the current one.
And thanks to Hugo for his kind advice.