Would the analogy "don't throw the baby out with the bath water" work here? This sounds like a Toro Flo-Pro valve. Is the solenoid dead center on the valve and the top of the valve screws onto the valve body? If so, throw that baby out. You may try tightening it down when you have turned the water off and have relieved the water pressure but, the problem will come back again later on. If the top has stainless steel screws (4 visible and 2 under the solenoid) and the solenoid has 2 stainless steel screws mounting it to the valve it would be easy to repair unless there is damage to the valve housing itself like from freeze damage. It is rare that type of valve will start leaking from the valve unless it has been serviced lately. Has it? If so, the problem is most likely an o-ring issue. Most valve are 1" and are threaded. You should be able to tell by looking at the inlet/outlet sides of the valve. If you decide to replace it no matter what, it is not that hard to do. First dig around the valve then about 2' along the outlet line which is normally poly pipe. There is a product on the market called a "stretch coupler" for poly pipe and I have found them to be great on replacing valves. By using it, you are able to connect your outlet side first, then slide the valve into place, and it allows you to thread the valve into the manifold (PVC). Make sure you use teflon tape on the threads. Keep in mind that there is only a short range that it will stretch so cut accordingly. Also watch out for your wires when digging. Hope that helps.