It sounds like there's some crud or sticky stuff in there. Even goo from fresh veggies or tree sap can form a kind of glue.

Have you tried a spray lubricant with a little more penetrating power? WD-40 or Liquid Wrench come to mind. I don't think these would hurt the bronze bushings.

BTW, have you been doing any super-heavy twisting with the pliers? That might be a factor, don't know for sure.

It takes a special tool to take the blade out. It's probably not a good idea to try. Leatherman's warranty is first-class; just send it and let them fix it.