What do you mean by it had oil issues when you purchased it? How many miles did you drive before the oil change? Had you been under the X5 to see if there was any evidence of oil on the undercarriage just prior to the oil change?

I always start with there are no coincidences. In other words-If it was not leaking prior to the oil and filter change the leak is most likely connected to the work just done. That said, in your case it doesn't sound like you can verify that their work was the cause. I suspect it is one of the unfortunate times that one is be better off just moving on unless you know an attorney that will handle the problem pro bono.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas