as captmatt points out, you can pretty easily and cheaply get a light seal replacement kit for one of these, and the job is pretty easy to do. you can also get various other accessories on places like the 'bay. but if you plan on keeping this K1000 for the long haul and using it often, I would offer a word of caution in using it before it has had a thorough CLA. normally for a k1000 its difficult to justify the cost of one, because they are so plentiful and usually not the main user for most pentax folks. most of us have had or still have one, but we normally turn to other bodies for various reasons. but since it seems like this will be your one camera, I would highly suggest that you drop the cash to have it CLA'd. there is really no better investment you could make into the camera and it will guarantee faithful and likely flawless service for more years than you will likely use it.
Eric Hendrickson is the resident Pentax man here, and I know of nobody better to recommend. the link to his page is in gofour3's post. do yourself and your camera a favour and have it done right.