this may sound silly--but make sure you have the solenoid installed with the 'I' and 'O' oriented correctly ( in and out ) If the solenoid is backwards it wont seal.
A photo on post #17 shows where the leak is coming from.
I've read a lot of solenoid problems lately. I hope those folks who are looking for solenoids, particularly Clippards, would have a chance to read these threads before buying.
Thread Title: "Just had TWO parker solenoid valves die on me in one day!"