I don't have time to search for the exact fit o-ring to save some spilled coolant and a couple bucks which is literally nothing compared to the thousands of dollars and time I have socked into my 4.6is. Mine has been well taken care of but after 10 years, things just start getting brittle and leak or break. Yesterday I had my passenger window regulator break (driver's already went). If it didn't have a 4.6is Dinan, I would've dumped my X5 long ago. The things that have gone bad on my X5 plagues all X5s - cooling system leaks, valve cover gaskets, window regulators, TC/trans. If these haven't troubled you yet, good luck. Mine was pretty much trouble free for the first year. I thought I got a 'good one' and was in the clear. Ha!