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Seems that the welding attaching the nut to the casing can fail. This dumps all the oil which a) blows the engine and b) soaks the rear tyre.

Had me worried there W, already checked, and mine is a 191. That list, however, tells me I am a 204. Have re-checked and it is wrong in my case.

https://www.knfilters.com/mobile/recallkn204