The early Wico pinball dollies had hydraulic cylinders. Later production used those gas shocks so common on automobile rear doors.

Those hydraulic cylinders are serviceable/rebuildable. Whenever any of ours went bad, we took the cart to our local industrial & hydraulic service center. Took them about an hour to rebuild it and they charged us just $40 for it.

The rebuild idea is a good one. Personally i just buy a new shock. I like the wico carts too. the one shown above is my favorite variety of pinball wico cart. Here's some info from RGP on the subject...

So i went to the Nappa auto parts store and bought a GM steering stablilizer. part number SC2913, about $30. Though not a perfect replacement, it did bolt in place and work decently. Used 1/4" bolts to hold it in place. The shock wants larger mount bolts. But I bought metal liners (80 cents each) at the hardware store to go inside the shock's mounts. Works pretty well. The disadvantage is there is dampening on the up stroke and down stroke.

I also have one of the new pin carts. It uses a Gabriel Red Ryder gas shock 738000. I guess I could have used that too, but the Nappa store didn't have one.

I have one that the shock is completely gone as well, but have really just gotten used to it and it doesn't really need it because you can set it down slowly by just slowly letting weight of the bar.

Incase you still haven't fixed it. Here is the info I found when replacing mine

https://pinside.com/pinball/forum/topic/pinball-lift-hydraulic-cylinder-replacement#post-2310532