Stuck Oil Plug - Ugh

Okay, I'll try to be brief, take full resonsibility for my screwing up (pun and all), and hope someone can offer a solution.

Several months after changing the oil on my Yamaha 9.9 (model year 2000) this spring I noticed a little oil leaking from the drain plug. When I put a box wrench on the plug to snug it tight I must have turned it too hard. The lower half -- the part with the brass head and some of the plastic surround -- came off. The upper half, which is completeley plastic and has a weep hole in the middle, remained in the oil pan. Somehow, I was ready with a container in the event I happened to turn the plug the wrong way; as such I was able to capture all of the oil as it drained out the weep hole.

While ordering a new drain plug I asked a local marine tech how to best remove the upper half. I tried his suggestion today -- using a bolt extractor. A little one that fit the weep hole only made the weep hole bigger. A larger extractor actually achieved some gripping effect but wouldn't budge the remaining part of the oil plug. I'm fairly strong but, as I may have crossed the threads (hence the initial leak) I was afraid of damaging the oil pan itself. I decided I ought to back the extractor out and seek your advice. If you think I should get really aggressive next time, enjoy a little laugh as that larger extractor now needs a replacement -- the first one is sitting under 9' of water.