Non-detergent oil is pretty much a thing of the past. If you want to keep the dirt out of the engine and not have to decarbon every year, change oil, put in good grade of non synthetic oil to help keep the rings scraping. If you do not drive much there is the possibility of rings not scraping and then there would be blow-by or fuel dropping past the rings into the sump and thinning the oil. Show cars need love and driving. If you look at the JCNA site you will see the St. Louis Concour winners drive theirs to and from the shows and on outings occasionally to keep them in running shape. That is part of the mystique of owning an old Jag. Yes, break downs are possible, but that's the quirckiness of British cars. Makes great stories at the shows and get togethers later. The oils of today are so much improved, they will make the car last longer on normal driving. Sitting and running is not normal and the acids will really work their way into the bearings and start the degrading process of which good money was paid to correct. Besides, what about the transmission, u-joints, and rear axles and etc. that need movement to lubricate. Most cars have to be moved a minimum of 25 ft per week just to coat the parts with lube. ( taken from a dealer lot with warning on new cars). You do not have to drive forever, but a few miles every couple weeks will keep tune in good condition.