I once sold a control system to BA Engineering for use in their huge hard chromium plating shop. All they did in there was refurbish undercarriages. I don't know if it is still there.
On one of my early visits I was being shown around and spotted a complete u/c leg, wheels and all. All the metal parts of the lower u/c leg were blue from excess heat. I was told that this was caused by a single heavy landing and I still find it unbelievable that one single shock load could cause sufficient heating to raise the temperature of such a mass of metal to a temperature of about 500 degrees C. I was assured that it was so but they also pointed out that it wasn't off a BA aircraft.
While the undercarriages may last the life of the aircraft they do seem to require sufficient refurbishment to justify such a large dedicated engineering establishment.