Yes, this usually indicates a worn engine, with worn crank bearings. I limped an 99 grand prix along for a couple years using heavier oil like 20W-50, but eventually the car needed a new engine. You could easily be in the same boat, especially if the seller has admitted to some leaks and replacing the oil pump.
Personally, this is one of the things I'd be on the lookout for when testing a used car, and it'* something that would indicate to me a worn engine and large bills in the future for a rebuild or a replacement.
If you've only had it for one day, is there any chance you can return the car for a refund? You're basically risking owning a car that will need a new engine sometime in the future, possibly in the very near future.
97 SE, teflon wiper blades, Dunlop Sport A-2 tires, Leather steering wheel cover, Pioneer DEH-P480MP mp3 CDRW head unit, Pioneer 12-disc changer, iPod hookup, Boston Acoustic 3 way 6x9'*, Boston acoustic separates in door pods, Alpine 4 channel amp in trunk. Magnaflow dual outlet muffler and Ractive stainless tips. Autozone rice pipe and K&N 4750 intake kit. Clear corner lights. Energy Suspension end links.