Leaking irrigation component

Gentlemen,
Please forgive me. I have been looking around a bit trying to find the name of the component I am writing about. I failed. But it is the place the irrigation guy goes to in order to winterize the system. This year it is leaking, perhaps two gallons per hour. The water is coming from around a white plastic component (see picture). I am handy with a wrench and not eager to pay a technician hundreds of dollars to repair. But I am not really sure what is leaking here. The plastic thing seems more like a cover than part of the water handling system. Advice would be much appreciated!!

The back flow device needs to be tested and repaired. It is leaking there to let you know it needs service. In my state you would need to hire a certified back flow tester to repair and re test it.

ct 18 is right but in my state only a lic.plumber can repair the device....

Geofd said:

ct 18 is right but in my state only a lic.plumber can repair the device....

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there should be a small plate riveted to the device it will give you a model brand name and serial number the model and brand name and the size of the pipe would tell you what kit to order