help with high oil consumption

Valve guides and piston rings is a very big involved job. The piston rings involves stripping the engine so you'd have to have all the kit before you even consider attempting it. Valve guides will require the cylinder head to be removed and then you would need to get new guides fitted by a speciallist.

I'd start with the gaskets you mentioned.

Just out of interest, what grade of oil are you using, and fully or part synthetic ?

My reason for asking is my 2000 E39 5281 lists part synth as an option, and is what I've used, (I can't remember if it's 10W 40 or 15W 40 as it never needs topping up), and doesn't use a litre in 15,000 ish miles.

My neighbours 2001 3.0 litre Z3 lists only 0W 40 or 5W 40 fully synthetic , and his uses about a litre every thousand miles.

I spoke to my main dealer when I first saw the difference in the handbooks, and they said BMW swapped them to fully synthetic around 2001, so they'd have used part synth in mine when it was new, and they didn't think I'd gain anything by swapping over now.

There are far more knowledgeable people than me on the forum, and you have the handbook for yours, I'm just wondering if the thicker semi synthetic may help your problem ?

I wasn't thinking specifically of leaks ..... of course fix any of those that appear.

I was suggesting that engines designed for thicker oils, will of course have a much higher oil consumption if thinner oils are chosen.

Good luck