Crankshaft Seal Upgrades. One of the few weak points of the Jaguar XK six-cylinder engine is the rear crankshaft seal. Early engines dont even have one, and later 3.8s and all 4.2s make do with an antiquated rope seal. These seal conversion kits use a modern rear seal for get this leak-free sealing! While such conversions are not new, these kits combine excellent quality and a reasonable price. Please note that the crankshaft must be turned down to fit the seal, so this modification is best made during an engine rebuild. The 3.8 kit uses all-new parts; the 4.2 unit uses a modified original seal housing; we will need your original back, in other words.