2016 rear wiper arm stuck

How do I get the wiper arm off of the post? I bought a new arm to replace the old one with broken spring but I cannot figure out how to get any significant pressure onto the arm to get it off. I’ve even soaking it with wd40 and I’ve tried leaving nut a little loose and squeezing with needle nose pliers but it’s stuck on. I know it’s a splined aluminum post and has some corrosion that binds it but the rear spoiler is right on top of this thing.
I looked into taking spoiler off but the arm will block the spoiler removal because the post feeds through a small hole in the plastic motor cover that is attached inside spoiler. It appears the arm was attached after spoiler.
Help!

 

Looking forward to an answer, I'm having the same problem.

Freaking rusty-ass Toyotas.

 

I was able to just pull mine off with some effort but I know there isn't much room with the wing wang in the way.

 

At Toyota service now. Technician said they have to take the whole cover off cause they don’t make a tool that can pull arm while cover is on. $90 for 30 min. job. I already had replacement arm from Amazon so it’d be at least twice that if you go with their arm.