Hi Chuck!
I was reading through your thread (I actually came here from the link you posted on OM's forums) and saw this pic, and thought to myself.... "gee that looks familiar". I was actually reading backward from the end somewhat so I had to backtrack further to confirm they were in fact the cheap valves like I had originally purchased for my setup.
The problem with these valves is they're not truly union valves in the sense we as reefer-types expect -- if you look inside one you'll notice that the "ball" that opens and closes the valve isn't actually held between anything when the union is removed! The union part itself is the other side of what holds the ball mechanism in place. That's why it leaks so badly when you remove the union. I also found that out the hard way. In my case I ended up leaving the valves in place and just adding normal unions near them -- they seem to work just fine when just used as valves. I honestly can't imagine them becoming impossible to turn, as if you have a problem you just need to pull the union off and the ball will be free to wiggle around inside the housing.
If you still have one, pull the union off and look inside and then wiggle the handle around a bit to see how bad they are.
So much for me thinking I got a great deal on true union ball valves!
Here's how my plumbing looks now:
