I've read that this is not uncommon.....I 'top' mine up to about 1/2" from the top when I check it, a couple times a year.
the next time I look, it's down a full inch from the top.
So it top it up.
then it's down.
....repeat ad infinitum!
( nope, nary a leak anywhere...not even a moist, dusty spot.)
is there actually evaporation of some solvents in the mixture? seems the vented caps in my car would allow a lot of this, but the level's been the same for a decade!
