Look on the bright side, better to discover a faulty master cylinder in the garage than on the road. Brake failure is no funÂ….but replacing a master cylinder is easy and relatively cheap.
True on the lesser of two evils bit-I'd rather replace the m/c, but not only do you have a potential brake failure, but you also have the erosion of topcoat and corrosion due to the hygroscopic nature of brake fluid.
