I run the ECS tuning 15mm spacers on my X5 and 850i and no issues what so ever with the 17mm head bolts OR the spacer them selves.
sorry to hear you are having issues.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S