The shock I got as a replacement is 16.75. I don't have the old one out yet, so I don't know for sure if it's the same length. It probably will be. The shock is original and hasn't been rebuilt, so I imagine it needs oil change, seals, and a recharge. I don't know anything about shocks, but that's what they need, isn't it?
I'll have to look on ebay for pricing. I'll give you a decent deal, but I'm not giving it away.
It bottoms out more than it used to, so I assume that it needs a rebuild. I was too lazy to get my sled prepared before the season, so now I'm just getting another shock to swap out and then sell the old one. Then I won't lose any riding time waiting for turnaround on the rebuild. I've already done the swap on the fronts, so I have some fronts for sale too.
There's the shock. Seems to be 16 1/2 or 16 5/8 center to center. Shaft is very straight and shiny; no pitting from corrosion. About 1/2" from the top mount there are a couple speckles and a tiny nick that you can feel with your fingernail. Usually there is ice buildup by the top mount, and it looks like maybe some sand or something was in the ice to make those marks.
Shock extends on its own, and I don't hear any squishy, bubbly noises during travel. I don't know if this is a characteristic of the Position Sensitive shock, but the first inch and a half of travel is stiff, then the next two inches are soft, and then the last two inches are stiff again. Seems to be a good shock. PM me with your intentions.