Hi, I'm researching which cam to buy and have been looking at some used cams on a UK dealer site. There are a couple which might be ok, but the problem is the dealer mentions `drum hours' and I'm not sure what this means or whether the drum hours that he mentions are good bad or indifferent. One cam has 1000 drum hours, the other has 3000. Does this mean that it's been lightly used, had average use or been thrashed?