Repetitive torque converter failures. The first time I pulled the transmission it took seven hours. The last time (#7), I had it on the workbench in 1 hour 15 minutes.
The torque converter shaft broke 6 times. The very first transmission failure was a sheared output shaft. A Jaguar parts dealer said that the original shaft was insufficiently heat treated. I installed the new shaft and it was trouble free. Another dealer told me (after the sixth torque converter failure) that Jaguar had redesigned the flywheel for these engines. Seems as if the torque converter shafts were breaking!
I purchased a new flywheel. (One must hold their breath when asking for a quote on Jaguar parts). Once installed, the torque converter failures ceased.
Another aggravation was the Lucas electrical equipment. They should have designated each electrical component in the car as "intermittent"!
The engine would frequently lose oil pressure on a sharp left turn. This was with a full complement of 11 quarts of oil. The pressure would restore itself quickly, but there were much concern about the damage being done to that $4,000 engine. I removed the oil pan for inspection. It was spotless and the oil pickup was clean. I noted the placement of an oil baffle that prevented oil from overfilling the left side of the pan on a left turn, but there was no baffle for the same function for a right turn. I fabricated one similar to the existing left side baffle and installed it. End of problem! How long had Jaguar made that engine?
A friend of mine once owned an XK. When I told him that I had purchased this vehicle, he stated that I would tow it more miles than it would be driven. How right he was! Renting tow dollies got so expensive that I finally fabricated a custom tow bar to fit the appropriately installed towing eyes on the front of the Jaguar.
However, I must say, when it was running... what an absolute joy to drive! Superb handling, plenty of power (despite it's weight) and fast!