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I want you to try to reset your windows and see if they hold the memory. First lower your windows and hold the both switches in the down position til you here a click from both doors. Then raise your windows and hold both switches in the up position til you hear a click from the door. This restes the window memory. If this works you may want to have your battery checked. Low voltage causes the windows to lose memory. Since it looks like your Jag is not driven much a low battery is most likely the cause of the windows losing memory.
Hopefully this answers your question and you accept. Positive feedback is appreciated and please let me know if I can assist you with anything else.
ASE Certified Technician
12 years Ford Lincoln/Mercury Jaguar dealership as a technician and shop foreman reparing all makes
Ok geat.
Let me know if you have any other issues with your XK. I'll be happy to help.