I used to be the parts manager of a Jaguar dealer. The V12's were nightmares. Not the engines, as much as the fuel systems. I'd say about 80% of the V12 Jags that aren't on the road are due to underhood fires caused by rotting out rubber connectors on the injectors, which eventually leaked fuel and caught fire.
We had one XJS V12 in the shop where the customer complained of a horrible fuel smell every time they turned on the A/C. Now those Jags used the old style GM axial A/C compressors, and those systems leaked back when those cars were new. A pound a year wasn't uncommon, in fact, it was expected.
There were some owners who hated that, or they were going on a trip and knew they were low on freon, so they'd jumper the pressure switch on the back of the compressor, then come in when the a/c didn't cool so well.
Well, the V12 engines run SO hot, that they had to run a fuel intercooler, which was basically a thermocouple setup where the incoming fuel was cooled by running straight through the high side of the A/C line. In this car, the pressure switch was bypassed, and the fuel intercooler developed an internal leak. The car burned the freon off in the combustion chamber, and when the fuel pressure exceeded the pressure in the A/C system, the A/C compressor was compressing FUEL
I've seen that happen maybe 4 times in the 5 years I worked there. The V12, when it ran, it ran beautifully, but when it didn't, good luck. They were neither powerful nor reliable, but they were smooth as silk.