Brake fluid
 

I recently checked fluid levels on my 1994 E320 wagon and discovered that the brake fluid was very low, although there were no performance issues. After adding an entire can of fluid (750 ml, this was more than I had ever added to any car), the reservoir was in the safe zone. After a brief drive around town, I returned home only to find a few hours later that the fluid had leaked all over the floor of the garage and the reservoir was almost empty. The car is currently spending the night at the dealership awaiting diagnosis. Should I fear anything worse than a leaking reservoir, hoses, or fittings?

Leak?
 

Where was the leak? By the front tire? rear? Under the engine?
More info for moreaccurate responses...:cool:

I'd guess at just the reservoir, maybe it has become dislodged from the master cylinder itself. Not a common problem, but since the brakes are working OK, I assume it'll be a cheap repair.
Good News Gilly

My gut says it is the resevoir grommets. Most likely losing the fluid from the rear two chambers and your front brakes were carrying the load.

Just a guess though.

Gotta be the reservoir, either the grommets or the hose that supplies fluid to the ABS unit. Both are cheap and replaceable-if you re-seat the reservoir, I suggest you drill a hole in the top of it and suck any/all fluid out-makes this job a LOT cleaner. Then replace the reservoir-it comes with the grommets you need from the dealer , and its cheap

MIchael means "suck with a vacuum pump," of course.
 

Brake fluid is just about the most poisonous fluid in use in automobiles, many times worse than anti-freeze, and R12 only turns into fosgen or mustard gas if you inhale it through a flame (e.g. a cigarette).