Yes, I might be overthinking it a bit. I have a picture in my mind of the tank splitting open and instantly ruining my engine but it seems like a lot of the time they just spring a small leak. Anyway you are right, I think I diminish the chance of rupture to almost zero with the E30 cap.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)