Buy new valves. If the present ones are a problem, get a better valve. I never had a Richdel (the original makers of Lawn Genie) leaker I couldn't cure with tightening, but you may have high water pressure (which means more failures if you just repair them) Rainbird makes a 075-DV with 3/4" threads
There's no knowing for sure what your valve is, since Lawn Genie stuff changes all the time now, unlike in the Richdel days.