[Kurt in NJ]

Post a picture of the boxes, originally they had glycerin, later on oil, the style of the box can give idea of era of manufacture date.
It will be interesting to see the shocks and boxes.
If the fluid has congealed it is likely glycerin, inside the shock is a check valve at the bottom,, at the top are 2 vent pins, the vent is almost just a scratch on the pin and is likely clogged requiring disassembly.
Removal of the adjusting valve would give access to the fluid inside, make something to hold the shock inside a container filled with the new oil and it will purge slowly out the needle valve hole while operating the shock.
I ended taking the shock apart totally to clean it, it was used but had no wear, tried just flushing it first but it wouldn’t purge air out ( had free play sort of bouncy then action at each end of stroke)
I am using multi viscosity tractor hydraulic oil for Kubota hydrostatic drive