Looking for advice before I start tearing things apart.

I have a 977H. I replaced the piston seals on the tilt cylinders which were completely worn . After replacement, I could park it for several days and the bucket would hold position.
I thought wow, its never been this good since I have owned it (30 years).
I have used it for about 20 hours, since , doing brush clearing and some boulder removal.
It has started intermittently not holding tilt while working.When this happens it is really bad,, put in a slight dig position and down it goes as if the valve was being opened. This doesn't happen all the time, and as to what makes it go away, I would say cycling the tilt valve back and forth (hard) seems to maybe help.
I also noticed that if I get the the third valve (rear ripper) to relief, I see some feed back (movement) on the tilt that I have never noticed before, but I don't use that circuit often

1), I don't see how the seals in the cylinders can have gone again so fast, I honed out any sharp gouges when I did the work, And, that is not consistent with the problem coming and going.
2) I seems to me that the problem is in the control valve. 
2A). It also seems like something is sticking open and should be closing down. The tilt circuit shows check valves??
3). When I look at the parts list and the service manual it is not obvious that there are any o-rings or seals that would be associated with this sort of behavior. The main spindles and housing are marked as non-serviceable and those part numbers don't seem to be available.

Note I am finding leaks and changing o-ring seals on the hydraulic lines as they have hardened from age.

Does anyone have experience in this area. I am open for suggestions.

thanks,
robert
 

One possibility, how well did the seal ring fill the grove? Some of my mistakes I remember well and hopefully don't make them again, some not so much. This one is a vague one, but I left a Teflon spacer ring out and the seal moved/rolled and failed very soon upon a rebuild. As I recall it could of been optional as if the spacer was used in the generic seal kit I used that fit any number of applications. So this may not apply to your situation.

Pretty sure the cylinders are fine. The Seal ring grooves were tight and I got the backup rings in on the right side.
The fact that it only leaks down some of the time... I am thinking that it might be the tilt cylinder relief valve is sticking. Thus when I cycle it all the way, everything starts working again? This would also explain the feedback from the third lever when it hits the relief as it ends up going back through the tilt relief valve?

Anyone have experience on working on these control valves?

robert

Load lock? Cat calls it something else! If it has one. This is something I would look for.