Did you check the valve stem or valve core? Get a bucket with just a little water and some dish washing soap (a good bit of soap) and wet the tire down slowly covering the entire area of the tire and along the rim watching for bubbles. If you have lift it will make this much easier. This should find the leak.Rear tire has a leak. About every 3 days it needs pumped up. I've looked it over and don't see anything in it. Any suggesstion?
I used Slime with a plug in my rear tire that started leaking and it lasted maybe a week before I started losing air again.I know there are a lot of doubters out there but use green slime (not fix-a-flat). Follow the directions on the bottle and your troubles are over. I got 10K to 12K on most of my tires so you're getting close to getting a new one.