Good progress. They do make an evaporator cleaner, you spray it into the ac drain hose, and it cleans everything. Changing out that unit and adding the cabin filter will help., brake fluid shouldn't get inside though, unless your master cylinder is leaking from the inside

The fumes might have got in from the fresh air ducts in the cowl. Since the prop valve was leaking inside the engine bay I dont see how else they would have made their way into the cabin. There's also a grommet and seal for the shifter assembly which sits above the exhaust that could have let fumes in, only other "hole" i can think of.

Start from the bottom my brotha at least you’re good but we need more vlogs

You smell it because the fluid was leaking & the smell coming in the vents but you can just pressure wash the bay maybe underneath to & remove the seats & rent a rub doctor & shampoo & detail clean the seats leave the vents blowing with the windows open for a few hours smell should go away the seats are still good just need a good clean

Id take the rear seats and trims 😅

Go B-series 😎

Well hey, if you have questions, feel free hit me up, im always ready to help