Yup. I have an '08 manual transmission Mazda3 and the parking brake handle broke inside. I took the whole thing apart, but no really good way to fix it. The good news, is that it was readily available from the local salvage yard. Because my driveway is sloped, I really need a parking brake.
Note, I took the old one off first. That showed me where all the tricks are, and special tools required for the removal. (at my local yard, you remove the parts yourself.)
Really easy job. And because many folks with automatic transmissions don't often use the parking brake, the replacement had very little wear.
Somewhere I have photos, if I can just find them...



Sorry there isn't a clear image of exactly what broke. It was the long plastic rod. I don't remember exactly what caused it. In an emergency it might have been possible to patch it up, but my local salvage yard typically charges like 5% to 10% of retail for stuff like this. In fact, the replacement handle came with the low gloss, matt chrome finish, same as the rest of the finish in the car. That shiny chrome parking brake button on the old handle was the only thing in the car that didn't match the rest of the trim on the instrument panel. That always bugged me. ha. All fixed.
As I look at the photos... Take the whole assembly out of the car first. You can disassemble the thing by just pulling the 'rubber' handle off the shaft. You don't need to depress anything. Mount the base in your vise and pull hard. After that you can remove the rubber boot, and see exactly what has gone wrong.