Got to drive that car more. A 2005 with only 36K on the clock? The lack of driving it and bringing everything up to normal operating temps is killing it. Gaskets, hoses, bushings and seals throughout are probably dry-rotting. You couldn't pay me to buy a XF with 5 miles on the clock that has been sitting for 15+ years. What a nightmare that would be. Don't let it sit... Drive it more.