What is the most leak free drain plug washer to use on a stock oil pan? I have a mopar reproduction hemi oil pan. I think it uses a 1/2" id washer. The plastic washer that came with it had a slow drip. I tried the rubber/steel washers from autozone and they leaked too. Copper works okay but not as good as the steel washer than I had on my old 440. I haven't been able to find a place that sells the copper washers in bulk and usually have to buy a variety pack of 3 to get the size I need.