I agree with CSK. I would be tempted to have a motorcycle place do them. $300 is just stupid. A good tech may be able to get close on the oil weight just by examining what is currently in them. There is a guy here who does offroad stuff and he quoted me $70 to change the shim pack for an air shock that had both nitrogen and oil. He had a machine that would show the difference in dampening rates before and after.
Shock Dyno?
It likely was- I am a bit out of my depth here. I have heard of a shock dyno but he didn't call it that at the time. My issue turned out to be something different so I didn't wind up revalving them. Ya called me out!
