hifi engine

Akai GX 210D reel to reel tapedeck

Does anybody know how to fix a too slow fast-forward and rewind function of the above mentioned tapedeck?
It is from 1976 and it has three motors.
AC voltage is set since 2005 to 240V due to the Dutch 230V standard.
Normally it could wind or rewind a 1800 ft. tape in approx. 115 seconds, but since a couple of months it has slowed down to at least 3.5 minutes, and if cold I even have to help the fastforward/rewind-take-up reel by hand!
I always keep the whole tape-path (guides/heads) clean.
I have thought of static electricity due to the use of plastic reels, but changing them with metal ones didn't change anything in the decks''misbehaviour'

With regards, Jan Otterspoor