* In my experience, the ABS isn't a very troublesome system. But when it starts acting up, there are a few basic things you can do to take care of many of the symptoms. Although these comments relate to many cars, they specifically relate to the questioner's R107 car.
* First, clean the speed sensors. One at each front wheel and a third at the differential. They attract metal particles and grime and then don't sense wheel rotation correctly. Also, make sure that the wire connections to the sensors are clean and secure.
* Flush the brake hydraulics once a year. I use a liter of ATE SL, a DOT 4 fluid, per car, per flush. Essentially you're clearing out the brake hydraulics using fresh brake fluid. Read some service literature on the correct procedure. Use a catch bottle at the bleed screws (rather than just blowing fluid all over the floor) to keep air from backing into system and to see what you're taking out. Note for cars newer than R107: if you have SBC brakes (MB > 2003?), you will need to disarm the SBC electronics. Suggest reading up on servicing SBC brakes, if this system is in your car. It can be dangerous if you don't do it right.
* Another ABS issue could be intermittant power supply. Put in a new over-voltage relay. You can "test" the original one, but it's not conclusive (in my view) and better to just replace the relay. And, make sure that the connections at the ABS unit are clean and secure.
* And here's a general suggestion for an older car. Replace all the old fuses with new ones. You'd be surprised how many "idiosyncracies" you can get rid of just by putting in fresh fuses. That's also a good time to make sure the fuses are the correct amperage rating and to clean the fuse holder contacts if needed (an ink erasure on a pen works pretty well). Good luck.