Possibly the prior owner added water only without the alcohol base washer fluid and it froze and created a hairline crack in the plastic. When we have freezing temps in California the people here aren't used to it and first thing to freeze is the washer bottle because they top it off with plain water
the plasic reservior may have cracked, however, the only fluid used ever, is the Porsche fluid. In fact, the orig fluid was still in the car when I bought it as the car was never driven in rain. All was good with the fluid level until a few months back when it began to leak mysteriously. I only use the porsche fluid and keep the litte bugger garaged. I think I know where James Dean got his nickname for his original sypder.....grrrrrr. :) In perspective, it could have been a tranny leak or engine leak, something more serious...counting blessings here.