It should not be leaking, but it may or may not be broken. FWIW, I remove mine in the winter. I plumbed it with 1" copper unions so R&R is fairly simple and very straight forward. I made an attachment with another union so that I can attach my air compressor hose to the sprinkler side and blow the lines from there. It is possible your breaker could have had some water left in it and froze, or it could just be a bad gasket. Pull it off and take it in to a shop to be checked out and repaired or replaced if necessary. These devices can go bad and not show outwardly, my city requires an annual inspection. These are done on-site by an approved inspector, usually a plumber, for a flat $25 fee.