I bought a new alto piece from Zinner last year, and I agree that at least that one tended to play significantly sharp in the palm keys. I don't remember that of it on an original alto Strathon piece I had in the 70's and 80's. Baffle looks different too, which tells me that it's not quite the same piece.
Other than the tenor 8 I got from phgsaxdude, (sorry, phgsaxdude) I haven't had any trouble with leaking from vintage pieces. This 8 from phgsaxdude, on the other hand, was pointed out by him as a particularly well playing and special piece for which I did pay well above the going rate. It appears that "well playing and extra special" means it leaks so badly that it hisses out of the top of the piece in the slider, and it's virtually unplayable. I won't be buying any more mouthpieces from this particular individual anymore, nor do I recommend others doing so.
That said, I haven't had trouble with the others I've bought used recently, but I do think you're better off buying a new one if you're concerned about abnormal leakage. The Zinner direct site is down, has been for months. If you call Zinner (they only admit to speaking German) they tell you to send them an e-mail, which they then don't answer. The site that Dr_sax suggests looks like you can probably order one, though their site clear doesn't seem to favor shipping outside of germanic speaking countries. I sold my alto piece to a deploying US Army band member that couldn't reach Zinner either, so maybe I'll give it a shot myself and see what happens. I need a new alto piece.