I own a 1972 450SL with 200k miles, lots of city driving. It's been in our family since 1976 and I've used generic brake fluid (mostly Castrol I believe) for all these miles and years. During this time I have had to replace the master cylinder once, all the rubber break hoses once and rebuilt the rear calipers once. Somehow the front calipers never needed replacing. I do have repair kits for them as I plan to do them on the next front break job. I should tell you though that it's generally not recommended for a backyard mechanic to rebuild a MB caliper.

I've always completely replaced the fluid in the front or back brake system whenever I'm doing a brake pad job since the fluid is so cheap and it takes me little extra time to do it. I don't want the brake lines on my old daily driver rusting through from inside out. Handy to have a turkey baster to pull out the fluid from the reservoir before adding new and bleeding. My Mityvac with the cheap brake bleeder accessory is good for spousal relationship. Somehow she does not enjoy pumping the brakes.

Bottom line: Can someone tell me if I should change over to Frontline's brake fluid as the first post suggested he would? I like the convenience of getting stuff at a local store rather than mail order for consumables like motor oil, ATF and even coolant. I have always used the special MB stuff though for wheel bearings and for lubing my 300D's sun roof (don't use generic grease, lithium or otherwise here!)

back to your question: I recall needing about 2 pints of brake fluid to replace the whole system since you need to bleed (and loose some). Better to get two containers as it's good to have some spare arround. Someone once told me that a bottle of brake fluid that's been opened (seal broken) will contaminate because it is so hygrophilic (absorbs water). I must confess that I did not follow that recommendation and just make sure to cap it tight. If you want the exact brake fluid capacity I can look it up tonight at home in my 450SL shop manual.

Good luck