Do you have a PCV system on the car????????? If so check it and make sure it is working properly,if not,you may want to put one on it and try that..........eaiser than taking the motor down and checking the heads...........
Also,you may want to do a "compression" test,run all cylinders,write down the readings,than,come back and put about 2 good squirts of engine
oil in each cylinder one at a time and run the compression test again.........if the compression goes up,than it's your rings............
David