The good thing about a purchase is that one day you won't have a car payment. And you can trade it in anytime without a major penalty. What you have going for you is that the MY02/03 have the 6 year/100k factory warranty. So it will be awhile before you have to borrow from your HELOC to pay for repairs.
Even with it, the 7 series is still a problem child. I sure hope you are more patient more than I am.