Hymac 580 C Staffa Motor Spool seals

[strontium90]

As some of you know, I have a 1981 Hymac 580C and since I acquired her in 2016, she has had a problem with less retardation on the slew, when swinging to the right...Swinging left is fine..She will also creep slightly to the right on level ground...while loading a trailer on an incline it is worse.

I have cleaned and checked the little check valves on the pipes between the Cross-Line-Relief-Valve and the Staffa motor and intend to remove the Cross-Line-Relief-Valve and check for dirt, check valves not seating, or weak springs in the 4 check valves in the XLRV.

If this doesn't solve it, I will have to look at the Staffa motor it's self.

Could it be the spool valve assembly seals in the top of the motor...looks like a similar arrangement to the Rotary Coupling?
Is it possible to remove the Top from the motor to check these, without removing the whole motor?
Is there any difficulties, like reconnecting the coupling or "dog" when reassembling and is it difficult?

I think replacing the seals in the motor look beyond me, but "must do is a great master"....Thanks in advance.