So I changed the oil on my 86 240 this past weekend, a first for me. Once the operation was completed I scouted under the car for oil leaks and noticed a drip coming off the oil drain plug. I wiped the plug clean and waited to see if the drip returned, and it did. So I get a drip off the oil drain plug about every 15 minutes. I have a few theories as to why I'm getting this leak which I will list below. Any feedback or thoughts on my leak problem will be much appreciated.

Theory 1: Bad crush washer. I didn't replace the crush washer and just reused the one that was on the plug.

Theory 2: I stripped the threads on the oil pan. I don't think this theory is that plausible as I didn't use all my might when tightening the oil drain plug.

Theory 3: Bad drain plug. On a previous oil change I had my mechanic swap out my old drain plug with an FCP Groton magnetic drain plug. I've read on this forum that some folks have had leak issues like mine with these.

Theory 4: Debris between crush washer and oil pan. The day I changed my oil it was kind of windy. I changed the oil in my driveway, which is dirt/gravel/sand. I fear that the wind may have blown dirt in and around the drain hole on the oil pan. I wiped the drain hole before putting the drain plug back in but maybe this was not enough.