Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
My best thing to say, would to put it on a cylinder & test it out; then maybe test it out in a pool. Still that is no guarantee it will work. I have seen problems with regulators not serviced for years,... then again, I've seen regs serviced yearly have problems too. Scubapro has moved their service intervals to every 2 yrs (100 dives)... 3 yrs being outside that time frame may be pushing it. I, personally, would err on the side of caution & have it serviced.