When I had a seized pedal and had tried all the wd40/leverage/etc stuff and it didn't work, i tried a heat treatment method. This involved pouring boiling water over the affected area very slowly, which actually was very effective, and the pedal came out with 1 turn of the spanner.
It could be worth a try, although in the pedal case it was easier because I had easy access to the problem area.
When I had a seized pedal and had tried all the wd40/leverage/etc stuff and it didn't work, i tried a heat treatment method. This involved pouring boiling water over the affected area very slowly, which actually was very effective, and the pedal came out with 1 turn of the spanner.
It could be worth a try, although in the pedal case it was easier because I had easy access to the problem area.