They are. Toyota still sells a rebuild kit.
Like many Toyota parts, they're first used on the higher end products like Land Cruiser. There were used on the LC Prado, so very proven with safety features I've well used (auto braking under certain conditions).
Here's a link on the how to:
Master Cylinder Rebuild - DIY | IH8MUD Forum
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2001 Limited 4WD - 346+K - SunfireRed\Thunder Cloud; - 265/75/16 Michelin A/T2s - Fat Pat's 1.5" BL - StopTech ANGLED rotors - In series 699 trans cooler, New Yota1 transmission, All new OEM suspension front to rear.