I would actually prefer a good used one to a new one, because someone else took the risk of the run-in, and if the used camkit is OK, then there should be no hardening fault or other issues with those parts. That is also my experience. I have had breakdowns with new stuff done correctly, so there must be quality problems as well, not only the wear pattern or lube issues. But there is always a risk... You are lucky if your client takes the risk, then you have your back free! My