Try getting it to budge first in the direction of tightness, just a little. You're in a tough area here, so I'm sure this won't do it all for you, but I routinely tighten first. Usually, a fastener that's been in place for decades will budge a bit -- say a sixteenth or an eighth of a turn. This way you're asking for initial movement in a direction that eliminates fighting the accumulation of crud (including rust, of course) on the exposed threads. Your impact driver works in this direction as well; whether you use it or not, stick to moderate force for this, at least at first, as clockwise movement is usually easier to get, and of course you don't want to twist it off. Any little movement is key; it will at the least facilitate penetration of the Blaster juice. It's no panacea but can give an edge in a tough struggle; good luck with yours.
