Hello there.i take it your talking about the servo.if so the main issue is that they leak vacume out.as it could be tricky to measure negative pressure at home I would say apply lightly regulated compressed air to check for leaks.if its air tight(don't go mad) and the body is corrosion free coupled with free moving parts I would say its a goer!!rob

It appears to be a goer Rob, I've also found a link since and tested it with a vacuum pump. After a bit of cleaning up and testing again it's working up to standard.