My mechanic (German guy, trained at the factory in Stuttgart, was Service Manager of the year in No. America in the 70s, - now runs his own shop) says that he ALWAYS replaces the ABS sensor when he replaces the brake pads. Cost is $6-7 each but cheap overall when accounting for the annoyance of some of what you guys have been experiencing.
I don't know whether or not this philosophy has helped us to avoid similar issues with our cars (neither of which are 126 models) but it certainly has kept brake issues out of our lives.
Scotts Valley, CA.
1993 300 CE Cabriolet (A124) 131K miles
1997 C-280 133K miles
2000 BMW R1100RT 69K miles
1989 300 E 216K miles (sold)