It's REALLY worth your while going to your LDS and asking them to show you how to follow @couv 's checklist. That will pay off over the long run in saving you from equipment problems just before a big dive trip.Thanks for all the comments. All the tech and mechanical stuff is over my head.
Oh. Just saw that you'd lost confidence in your LDS. Well, open a conversation with @couv . He'd be happy to walk you through it. The only part that doesn't apply to your Sherwood is the intentional air leak from the first stage when you submerge it. Just invert a shot glass over the rubber stopper that's bubbling. You should collect 1/2 to 2/3 of a shot glass with of bubbles in one minute. That's normal functioning.