I suspect this is similar to my XJ8 which likely has the same transmission, my dies at 125,000 miles. Once it goes into limp mode, the trans is toast. The dealer would not repair it, a trans shop would not touch it either, as no spare parts are available. The only repair is to replace the trans. I scoured recyclers around the country for a replacement, and settled on a 32,000 mile trans for $1700. My local mechanic installed for $1000 plus the very pricey oil - 8 qts @ ~$50.00 per qt. I have added 30,000 miles since and had no problems.