Wow Opto, thats rare to say the least... and to BOTH of them simultaneously?

I'm just spitballing, but I wonder if it's a combo of condensation in the fluid (brake fluid is hygroscopic) and being frozen in your garage? I'm guessing its not heated and you're way up there where theres more mooses than peoples

No matter, re-build kits are less than $20 and it's a cinch to pop out the snap ring to swap the pistons, flush and bleed with DOT 4 like the cap says. EZ PZ.