If you have replaced the valve seals, then someplace else is drinking the oil. Make sure you don't have a pressure leak anywhere. Excessive oil consumption will destroy everything from the headers to the muffler. Excessive oil consumption is tell-tale blue smoke. You better hope that it is not the piston rings because the engine will have to be dismantled almost completely. I wouldnt let it get past 1 qt per 750 miles. Perhaps, you should change to a thicker viscosity like 20W50.