I suggest you replace the two rear wheel speed sensors, or at least the left one that also drives the speedometer. That is more to rule them out than anything. It is simply the cheapest thing to do to eliminate them as a cause.

The comment that I picked up on was that sometime the speedometer went off with the light (indicating the LR sensor) and sometimes it didn't (indicating something else).

Another possibility is that there is a fault in the wiring harness between the sensor(s) and the ABS controller. That fault appears to be intermittent, and could be difficult to locate, but if it was found it could look like chafed or worn wires at some point along the harness.

It depends what tests were done in the original diagnosis, but the sensors would have been the first thing to check. If a test showed that it wasn't the sensor, I can imagine that the module would be targetted as the next option, partly due to the difficulty in finding a problem in the wiring harness. It is unfortunate if you paid for a module that you didn't need, but it may still have been cheaper than the labour cost for tracking a wiring fault. I would think that the shop would be participating in some form of policy settlement that gives you a financial break. Whereas they may have replaced something that wasn't faulty, sometimes that is cheaper than doing further diagnosis due to today's high hourly labour rates, particularly for troubleshooting. The fact that they readily gave you the old parts suggests that they aren't trying to hide anything, so talk to them about the next steps, and the costs of what you have done so far. Tell them that you are concerned with the rising cost of this repair, and want to know that you are both in it together. See how that goes.

I don't know the testing procedure for the module, but I wouldn't be swapping them in and out now. I think the cost of doing so, including coding, is more than the value of the module. It may be possible for the module to be bench tested by someone familiar with overhauling them.

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