Question
I overtightened the small flathead screw that lets one manually turn on / off the sprinkler flow from a 10+ year old brass Superior valve. It now rotates freely and leaks to varying degrees depending where it is in its rotation. Is there any "easy" way to repair this vs. cutting the valve out of the plastic sprinkler system? Thanks in advance!

Answer
I dont know of an easy way to fix it.  I have replaced the entire top of the valve before, but it was because I had the spare parts around.  You may be able to try using a little bit larger self tapping screw to replace the old one, but it probably won't work very well or for long.  Its probably best to replace the valve.