The accumulators seem to be the only part in the system that wears out regularly. Other things may have issues from time to time, but the accumulators are the regular culprit.
And they will fail both ways, as I have found out.
First wagon was super bouncy and soft, bobbing along like a car with only springs, no shocks. Was saggy in the rear, and would not raise via the linkage from the valve.
Current wagon was super harsh, with the requisite "whamming" that you speak of. However, it would still raise and lower via the linkage some.
Accumulators took care of both issues.
As a side note, on BOTH wagons, not long after replacing the accumulators, the hydraulic high pressure line blew out! Within a month or two. So, if you see oil slung on the underside of hood, or somewhere in the engine bay, you might want to have that line repaired. They will cut the ends off and braise them on new hydraulic hose. Others I believe have had removable fittings, but mine weren't like that. Cost was around $60 bucks, so you might want to do it anyway. That fluid ain't that cheap........

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John