My dart sat for 4 years. The mc seeped inside the car. No smell at all. But there was liquid and gummy desolved paint under the OEM carpet.
I too have the same situation but I can positively say it is my right rear wheel cylinder leaking. Down 1 inch of fluid small resivour in a few months. Mut have just started as in Jan or March I was under the rear and would have noticed it.
The front and rear sumps are connected bya gap between the pistons so you can have a front leaked that will drain the rear sump. Something to look for.
IIRC front brake mc piston closed off a port between rear brake piston when you apply the brakes. The fluid between the two pistons is what applys the rear brake piston. In the event of a front brake failure the two pistons will touch applying the rear brake piston.
I believe that the port I am thinking about can pull fluid from one resivour to the other. (Just not 100%sure about that.) Internal leaks can for sure.
