Land Rover Repair: ABS Sensors in 96 Discovery, dry pavement, air gap

Question
I have a '96 Discovery that has more than 161,000 and (knock on wood) it's still running...barely.  I took the car to the dealership to have the front brake pads and front rotors replaced.  When I got the car back, the brake pedal started to shudder on flat, dry pavement.  I took it back to LR and they said they "fixed" the ABS Sensors.  About three days later the shuddering started again and I took it back to the dealership.  That's when they told me I needed to replace 2 of the ABS Sensors.  Are the ABS sensors really broken or are they trying to squeeze $1400 out of me?  If they are broken, then why didn't they tell me that the first time I came in.  I think it's all a little fishy.  I've written a letter to the dealership and also LRNA about this issue. As you might guess, the car is out of warranty. The brake pedal shudders on an irregular basis, but almost everytime I get into the car it does it. How long can I drive with the ABS like this?  

Answer
Try to push all the 4 sensors (with little knockings) to deeper. If some is moved, there was too large air-gap.
So knock carefully until it stopped (if no movement at all, than no problem with air gap).

Then use the car for a few days, than check the movements again.

Otherwise you can go normally if you remove the ABS fuses.

1400$ for 2 sensors? And nothing else material needed? It's too much. Change of a sensor about half hour, and the sensor's price is more cheaper I think (about 300$ per piece)