Jcb 803 plus excavator (3 ton) track motor problem

Hello everyone. I have a JCB 803 plus excavator (3 ton) and when you first use it the right track quite often jerks and does not go want to move at all even if the revs are up. When warm it really doesnt behave the same as the left.It can be sluggish. There is no noise and the rest of it works fine. The track isnt tight.It has had a hydraulic oil change.There is enough oil. The pump makes no noise at all. Is there a valve that is sticking to the track? The controls are very responsive and dont seem to have play. Is it the track motor itself thats had it? Any help would be very appreciated. John