Kubota kx161-2 issues

I’m having some hydraulic issues with my Kubota kx161-2 excavator and am having troubles diagnosing it. 1- left track has heaps less power than right track and won’t track straight. I’ve replaced swivel joint seals, and outputs of pump has been switched between tracks with no change. This leads me to either the final drive or an issue with the control valve. The left and right motor case drains dribble at the same rate when dead ended. 2- The functions fed by a small gear pump (blade, swing and slew) go weak intermittently. Prv’s are not sticking. Because of these 2 issues I’m thinking that the control valve is somehow bypassing internally. Is this possible? Are there parts or seals that wear on control valves that could cause this or similar issues? I use my machine on my property and it’s been like this for a few years. I make do with it but would love to get it running right. I’ve found it hard to get a local plant mechanic to check it out. Any ideas would really be appreciated. Thanks!