I had some very stuck parts on a Pfaff 145 I've been restoring as I find parts. I used PB Blaster, time, and some heat to get the parts to finally loosen up enough to get them apart without damaging them. I would apply the PB Blaster let it sit for a while then apply some heat (from a blow (hair) dryer and later a paint stripper gun set on low) gently try and pry up the stuck piece and repeat. Over time the parts came apart as the PB Blaster worked farther and farther between the stuck parts.
https://www.homedepot.com/p/Blaster-11-oz-The-Original-PB-Penetrant-16-PB/205178591 https://www.amazon.com/Blaster-16-PB-Penetrating-Catalyst-11-Ounces/dp/B000I2079E some quick info.