Most decks in those days spec'd about 5 minutes to FF or Rew a T-120 tape.
On RCAs and similar Hitachis, replacing the idler assy fixed FF-Rew problems. More to it than the rubber idler tire, there is a clutch on the pulley that mounts on the reel motor shaft, that begins to drag down the torque as it wears. Has to have a little drag on it to make the idler shift from FF to Rew but over time they get worn and have sticky rotation if you take it off and turn the pulley by hand. New ones are smooth to turn.
Here's an old pic someone posted of the idler assy Studio Sound used to stock but they are discontinued nowadays.
