Have the valve stem seals ever been replaced? If not, I'd advise to take this opportunity to replace them since you'll have done 80% of the tasks and just be one step away to reaching them.

I have for rent all the tools required (including the engine timing tools): https://xoutpost.com/classifieds/bmw...-5-months.html

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.