My guess is your valve added pressure to the system until it maxxed out and thats why the ride got hard. Mine does that occasionally when I load it. Not sure what you mean by actuator, but its definitely not your accumulators.
I would rebuild the valve. 300TD on here has kits.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660