re: Penetrating fluid - I would use plus gas if you can get it, much better at penetrating than WD40 in my opinion...
You can get it at the usual motor trade outlets, or at RS components (they have got trade counters about too)
Plus gas (overnight) + big hammer =
Can you get a ball joint splitter in there? or even an impact wrench??
(Sorry not done this job yet, don't know how much space you've got !)