I had been driving it for several years and never opened it. It just started leaking. It was half empty when I checked it, topped it off to about 1/4" from the top. I doubt the level has anything to do with it. Something odd is going on.
Not that topping it off is definitively the cause, but (with all diagnosis usually) go back to what changed before the problem started. Remove some fluid and see if the issue persists. Doesn’t need to be full anyways. If the brake pads/shoes are half wore out, the fluid would be noticeably lower than full anyways and it would never be an issue.
Also, if your brakes all work good and no need to crack a line or bleeder and you want to help preserve the system (at whatever age and level of corrosion is present throughout the brake system) replace all the fluid in the MC with new. Suck it dry and put in new.
Then check it after some drives. It’s probably brown again. Replace again. And repeat until you’ve effectively introduced a good qty of new brake fluid into the system.
Brake fluid doesn’t “wear out” quickly from use (like other fluids that get broken down due to friction/ rotating parts etc). But it degrades from absorbing moisture and moisture corrodes the (also cast iron) calipers and wheel cyl etc. If you can get the old brake fluid out, a flush is the best, but I just described what I call a poor man’s brake flush.
The new fluid will mix with old after a bit of use and dilute the old fluid with new. The more times you replace some of it, the more new fluid is left in the system.
Not perfect but a cheap easy 5 min way to keep your brake fluid fresher with less moisture.
Sorry not lecturing you but when you add old car and never checked or replaced fluid you get problems quicker than old car and fresh fluid.
Same concept applies to other systems and fluids as well.
I don’t have definitive proof but one example is the surge brakes on our boat. It’s not uncommon for the mc or wheel cylinders/calipers to have a short life compared to a car. I replaced plenty of <10 years old boat trailer components back in the day. Current boat is 19 years old. Bought it in 2009 and shortly thereafter found brown rusty brake fluid in the MC. I’ve been doing what I said above 1-2x a year most years since then and 19 years later the fluid is barely darker the next year and there’s no buildup of rust crud in the mc. I’ve probably put $15 worth of fluid in it in 15 years but haven’t had to do any brake repair yet. They still work.
