Recently I found my YJ power steering reservoir was leaking. Much to my surprise no one makes these. Cracked ones are actually a common problem. eBay sellers are also very aware of this, as good used ones were near $100.
So this left me with a few options:
I chose option number 3. The 87-90 XJ 2.1 and 2.5 Liter Reservoir is pretty close to the YJ reservoir. The XJ reservoir does take a different cap / lid so you will need this as well. Reservoir and cap was about $30 new. As you can see the XJ reservoir uses the same size hoses as the YJ:
It does mount differently though, so you will need to make a couple brackets to mount it. Both are essentially "L" brackets, but the bottom one being a little different. Here is my bottom bracket:
Both brackets installed: