John Deere 435 round baler twine arm cylinder

I have a 90's model 435 round baler bought new. I noticed last time we rolled hay the twine arms, when returning back to cut twine the arms were jerking real bad. Changed fluid and filter in pump, still jerking bad. It will put an extra amount of twine on that side of the bale. As far back as i can remember we have not had any problems with the cylinder or pump, all original. Can someone on here steer me in the right direction to check first to figure out what I may need. As old as this baler is I may need to replace both the pump and cylinder. Everything functions and cycles as it should as far as I can tell it will make a roll but just wanting to get the bugs out before this hay season. 

 

Thanks Donny

John Deere 435 round baler twine arm cylinder