Here is a master cylinder off a 1984 Yamaha RD350LC that has never had the fluid drained or replaced since it left the factory. This bike has also been in storage for the last 10 years..
You dont stop riding when you get old, you get old when you stop riding:)
My NS400 looked like that when it came in from Japan. I just blew it out with the compressor and bled it back up and it was perfect. I never even disconnected the brake line.