seized spark plugs

[doodah man]

I just went to change out my spark plugs and couldn't get them out. I only tried two and didn't try any harder than I could pull a 3/8 in socket wrench, because I was worried about them breaking off or stripping the hex part. All the visible metal on the plugs is rusted pretty good. Based on PO records, they've been in the truck since 1996.

I'm thinking WD-40, a little more leverage on my wrench, and maybe trying to pull them when the truck is warmed up.

If anyone has run into this problem before and has any advice on getting them out without making a bigger problem, I'd appreciate it. Thanks.