If it's "like new", it should have come with a cap, no? the little quarter-sized piece of metal that screws into the hood?
As for whether you "should" use a filter, do a sesrch of this forum, dpreview, or just Google 0 you'll find a pretty much weekly debate on that very topic. Some people like them because they are worried about scratching their lenses. Others don't like them because they are worried about loss of image quality. In reality, they probably really have very little effect either way (that is they don't protect a lens against very much, nor do they affect IQ very much). As far as I'm concerned, the only point of buying a filter is to lighten your wallet, but the filter will weigh more than the cash you spent. So I consider that a net loss.
Last edited by Marc Sabatella; 08-03-2009 at 11:26 AM.