[THEFERMANATOR]

Originally Posted by macojoe

When all else fails just unscrew the 3 screws that hold it on the boat, pry off the whole thing and replace, cheap and easier then screwing around with the old one. Make sure you use 5200 to seal all when you replace.
When putting the nut back in put some never seize on it and never have this problem again!!

MJ, he's talking about his lower unit's drain plug not the hulls. Like above posters said, drive a slightly larger bit in there(torx would probably work best). And hit it a few times to try and crush the seal down to relieve some of the pressure on it. Be careful using heat though as the aluminum threads tend to stick to the stainless when they get hot. Heat it and let it cool, do this a few times to try and let the disimliar metals expand and contract against each other as this will also help loosen it some.