Porsche dealership want $2,300 wants to replace brake booster and master cylinder

[99 Boxcutter]

So, my brakes are doing this thing where the pedal becomes rock hard after a few miles and completely locks up, rendering the car undrivable. I have to wait an hour or so until the brakes go back to normal.

Porsche dealership says it's *MOST LIKELY* the brake booster leaking onto the master cylinder and they want $2,300 to fix it which sounds insanely high because I went onto youtube and found THIS VIDEO where the guy made replacing those parts look fairly simple.

I'm wondering if I should try this myself or take my car somewhere else, but I'm worried about the dealership's diagnosis because they said they weren't completely sure until they dove into it. I'd hate to replace these parts and have the problem persist.