Classic Winnebagos & Vintage RVs

Hey, Blakradish here.
My brakes are locked after what I'm assuming is a fluid leak.
Everything was great when I parked it for storage, but after a few months of sitting, I started it up (first try), put it into drive, and it wouldn't move an inch.
It's not my transmission because it tried to move forward but it felt like it had wheel chocks under the tires, which is definitely not the case.
To my memory I've never engaged the parking brake, but when I press the button on top nothing happens, but I'm unsure if I'm doing it right.
I did screw around a bit with that weird vacuum thingy behind the drivers seat, but I don't think I broke the seal.
I have mobility issues, and it's really hard to get under the drivers side wheel to fill the master cylinder.
I have a theory that the brake line leaked, and due to lack of hydraulic pressure, the shoes fell onto the drum and locked the brakes.
Thanks for any help you can give, y'all helped me out a lot when I was getting it overhauled and updated.
I'm ready to get back into travels now that this damned plague is getting under control.
I hope everyone out there survived the past year , and I'm looking forward to engaging with you again.
🐝

Nothing happens when you press the button on top of... what?
If the parking brake was engaged, the lever to left of the seat would be pointing straight up.

The parking brake.
I'm really not sure if it's engaged or not.
I've never used it.

Thanks.
Could my theory about the shoes engaging the drums for lack of hydraulic pressure hold any water?

Got  photo of your brake lever in the cab?

I'm going out there today and take pics of my handle.
Do you have any idea where I can get my power steering box rebuilt?