I don't think you have done near enough troubleshooting to start throwing parts at the problem, especially since at this juncture there is no problem.



Right now I would focus on the burning smell.

If it is connected to the valve cover gasket it would be a were that is shorting that could cause the burning smell.

Something burning--what did it smell like.? Rubber, plastic, coolant, burning oil etc.?

How long did you try to start the engine before you smelled something burning? If you cranked the engine over for a long time the smell could have been the starter or associated wiring, even coming from the battery cables.

Was there any indication where the smell was coming from?

Any smoke?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas