all engines burn a little oil. Briggs even puts a specification in their repair manuals (at least they used to). if it is no more than an ounce or 2, i would leave it. Run it till it dies. if it is really bad, you can rebuild it. There are no rebuild kits with everything you need. at the minimum, a gasket kit with seals and new rings. however, everyhting should be mic'd out and compared to the service manual for wear. check the cylinder on the thrust side as well as non-thurst side, check in 3 spots each (top, middle, bottom). you are checking for out of round and for barrel shape. check the con-rod for wear at both ends. may have to do an undersize rod. check crankshaft for wear. check valves etc. also check the head for warpage. easiest way to do this is use a fine piece of sandpaper on a flat surface and lap the head. if there are high spots, it will show.
sorry for rambling