I've used quite a few solenoid valves, both the cheapest of the cheap from the Chinese sellers on eBay, and well used ones purchased from eBay or salvaged myself. I don't remember every running into one that leaked. I haven't used an automotive solenoid valve, but it wouldn't likely do much good to a car if it leaked, so I'd guess they have that sorted. One thing to look out for: a solenoid is just an electromagnetic coil, which is used to drive a linear actuator. So be careful that you are getting the entire actuator + valve assembly, rather than the coil alone or the coil+actuator. You can purchase replacement solenoids for a solenoid valve, but the solenoid alone won't be super useful for your application.
Here is a cheap solenoid actuator:
That is not what you want (though they are a useful and fun thing to play around with!)
These are solenoid valves:
Those are the sort I was using for my applications which required higher pressure and flow, so I haven't experience with the small and cheaper ones. But this common and cheap style looks very interesting:
