I'm going to replace the valve stem seals using rented AGA tool and a rope (to keep the valves up instead of air). It's not difficult, only tedious and time-consuming. Replacing the valve covers is the most difficult component of the whole project. Here's a facebook group for rental and description of the rope process. The rope technique makes the whole project much easier - no air compressor is needed for the project - and you can take your time and do the job carefully. No rushing due to fear of losing air and dropping the valves. The rope keeps up and prevents the valves you're working on from dropping.
https://www.facebook.com/groups/BMWAGAN62TOOLRENTAL/

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