I have a 2wd 1993 Chevy Cheyenne 2500 with a 4.3L engine and an auto trans. There is oil leaking from the EGR Valve and I am wandering if this means the EGR Valve needs to be replaced? Also, about every three to four months my engine starts running rough and my #3 cylinder seems to stop firing. I replace the spark plug and everything is fine for another three to four months. Could this be related to the EGR Valve?