It seems you may have had one circuit not functioning when you picked the car up and the other failed when you were driving it. If this is the case, fixing the one line you are aware of that blew when you were driving will at best restore the condition you experienced when you picked the car up.
The braking system is set up to give you one circuit for the two front brakes and one rear with the other doing the two front brakes and the other rear. Blowing out the front brake line hose disables both "circuits" as they really only back up the master cylinder and only one hose connects the hydraulic system to each brake. The master cylinder has dynamic seals, meaning things that seal when the piston moves inside, and these things wear out over time, more so than the steel tubing or hoses, which see pressure cycles but very little wear and tear. The brake hoses and steel lines are therefore not usually considered high risk for failure items and the cost of having check valves and the like in the calipers to allow multiple lines to each brake would probably lead to more reliability problems than less. And definitely more cost.
When you found the leak, did you first fill the master cylinder reservoir all the way up? The reservoir is designed to fill the rear compartment by overflowing the front one. The partition is there in case the line going to the single rear brake, or the clutch which is fed from the rear compartment, develops a leak and the fluid is all drained out. You still have the front compartment and the brakes it services left. The front can also drain if the line to the other rear brake is lost without taking the whole brake system out.
So, it would seem you have a leaking clutch hydraulic element, or a bad rear brake caliper or hose/steel line that is causing your second circuit to be inoperable. This could explain the pulling you experienced if it was not too violent. Since rear brakes, even when they are new, don't do too much of the braking duty with car going forward, it is unlikely really violent pulling (that wants to wrench the wheel out of your hands) is coming from the scenario I described with one rear brake not working due to a hydraulic leak.
I would also suspect both rear brakes are basically non-functional if the car has been sitting idle for years, and that you have a poorly performing front right brake caliper, also from being idle for years. The black stuff you see all around the brakes and wheels from burning off the pad liner is full of carbon, which is galvanically active when wet and in contact with steel, so it causes corrosion that can bind things up pretty good if it is left to corrode for years. Daily use prevents most of this from being serious, except on those rear brakes. Even with daily use it is probable that the rear brakes will eventually stick due to corrosion since they are so inactive compared to the front ones.
This got a little long, but your issue is a safety issue. You are much better off with an automobile that won't go than a car that can't stop. While brakes will cost you a few hundred dollars to completely rebuild/replace, it is the only way to go. Hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)