It’s common fault for one reason. Most cars never ever see the ABS system activated. What happens AFAIK is that when the ABS is activated pressure from the hydraulic accumulator is released. The pump then has to kick in to re-pressurise the accumulator. But, the pump has sat idle since the vehicle was built & has now siezed up 😥 So you get one activation of the ABS but get a warning light that refuses to go out as the pump cant re-pressurise the accumulator 👿
It may not be dangerous to drive but I’m not sure about the legality of driving the car with part of the braking system inoperative. There were prosecutions for this some years back. From memory, it involved the Sierra Cosworth, who’s ABS came with a switch to de-activate it.
Can’t help with getting the unit fixed. £1300 quid seems a bit steep. I’d hunt around, someone’s got to be fixing the ABS units. Where there’s muck there’s brass.
Good luck, D.