Finally got the ABS working again! Gave up on trying to source some new genuine front wheel sensors and installed the Intermotor ALS1431
aftermarket non-genuine E28 version length ones instead. Very happy to report they work a treat first time straight out of the box, no dramas at all. Bosch can go suck it as far as I'm concerned.
Did require a bit of jiggery pokery to re-route the cables from the car's wiring harness to reach the new shorter plugs from the wheel sensors, but with some proper fabric wiring harness wrap and careful positioning of the cables, it all looks perfectly factory fitted again, and the best bit is no more orange light on the dash and no more pulsing brake pedal when there's no need at all from lack of trigger pulses from the proxies to the flags on the trigger wheels. Stand on the brake now though and the wheels no longer lock just as they're supposed to. Very happy to have working ABS again coming into winter.
Replaced both front wheel sensors and the right rear too. The left rear was done over a year ago when it was discovered the state of the pulse generators was so bad, there was nothing doing except replacing all four. The insulation shielding had completely cracked off the entire length of all four original cables, so clearly there was so much EM noise polluting the signal with no shielding, they were no longer capable of being a reliable trigger for the ABS computer.
While in there with the rear seat shells out to plug the rear sensors in, also fabbed up some shaped bits of aluminium sheet to go behind the rear seat base wall, glued in place with epoxy body adhesive to repair the cross-threaded screw holes for the seat shell front brackets. Not a major thing, but ever since I put in a lot of work to fit premium speaker pods in the rear parcel shelf, it has always shat me and played on my mind that when reassemblng everything in the rear seat area, I knew that a couple of the rear seat shell anchor screws would spin and spin endlessly and never take up tension properly. The wall thickness of the seat base is paper-thin and doesn't take a lot of screwing-unscrewing-screwing taking the seat shells in-out again over many years before the metal is so chewed it can't hold a self-tapper anymore, so this had to be addressed.