TMI did the research and published a memo back in early 06. I'll forward you a copy of it. Rich Goodrow an s197 specialist and a technical specialist with TMI worked the testing. I spoke with him directly numerous times. I thought they outlaid something in the ballpark of 16 or 17k in testing.. Don't quote me on that, drawing from memory here, but it was a large multi K number.

Basically, part of the problem is that the single solenoid is unforgiving in those drivers that are creative in it's use.. and for that matter fast at making adjustements on the fly.. My understanding is these people back wash (rush backing of fluid) the Booster (vacuum back rush in regards to the booster) and ABS controller and it fails partially or entirely.

There was another example of full failure on what I thought was nearly a 100% basis (again drawing from memory) when the single solenoid is engaged, and the user stayed mashing the pedal, once the lock was released, inherently so was the pedal and it appeared as though a double release occured. Backwash again occured and tossed the ABS light intermittantly, in some cases it was a constant, and in others the ABS was gone altogether.

So there are some specifics and an abbreviated list of what I recall from Rich's document. Apparently location of the solenoids right off the caliper and the use of duals is far more forgiving to all components of the braking system.