Random ABS Activation Problem

2000 Oldsmobile Silhouette, 130K.

Lately the ABS will activate on dry pavement at slow speeds - as in when coming near to a top. It happens randomly. It might be more likely when turning right, but can also happen just going straight.

The ABS warning light is not on, but does light up for the self-test whenever the van starts. I had it to my brake shop today and as far as the computer is concerned all is well.

The basic mechanicals of the system (pads, shoes, drums, rotors, etc.) are all in good order, including recently flushed and full fluid. Over the life of the van, the fluid had been regularly serviced.

I did recently have to free up the rear brake adjuster screws (one frozen, one sticky) and replaced both front flexible lines (one was routed wrong and rubbing on the inner fender well so I just replaced both).

The rears were readjusted and the fronts bled (first gravity, then vacuum pump). That doesn’t much matter anyway b/c the problem started before this work and it was reports from my wife of odd braking behavior that got me onto brake inspection.

My Haynes manual is useless for this. Internet info is basically full of ambiguity about it given that there is no warning light and thus no diagnostic info.

My brake shop tells me everything is fine as near as they can tell. Any ideas on how I go about sorting it out?

Just FYI: I can’t inspect or clean the wheel speed sensors b/c they are integrated into the hub, and those will run a minimum of $100+ each. If there’s a shade-tree way to test them though I’d be thrilled to do it (I have a multimeter and know how to use it). The wheel bearings themselves show no obvious signs of problems by normal inspection methods.