I think that's the least they can do considering what's happened. They need to get this sorted for you.Well, since posting the garage have said they are a bit suspect about the abs test/refurb, so for free, they said they are going to use their golf abs module as a donor & see what happens. If it improves then my unit's fee will be refunded & the car might start behaving. I really don't know otherwise.
Your ECU idea is interesting. Unfortunately the two front wheels apparently have bound on with car started, but cold, literally after meters of driving, so even more confusing to me.
ECU has zero control over anything brake related.