Hey Phil!
Mine has too many rings as well, but i'm OK with that. Especially if it gets me out of the proverbial!
Good fun too
I have several brake boosters, and it has taken all of em to donate something that the other ones had which was stuffed. The best one was found by a friend of mine & cost me $20. While it was 'sound', it had suffered from poor storage which had caused some corrosion in the valve shaft. Another one I cut a section out of both ends of the shaft to see/understand what was happening inside. This provided far more details than reading the manual!!!
I see your booster has the breather attached to the unit. Mine has the breather remote on chassis. Did you just put yours onto the booster body for testing purposes???