I have a 98 Chevy Malibu with 124K on it right now. I currently use Vavoline MaxLife 5W-30 oil and change it every 3000 miles. I was thinking about Switching to that Mobil Extended Performance 15K oil - is this a good idea? I've heard about problems with older engines leaking with synthetic or something like that. Also, if I do switch, what's a good filter to get? I mean, the thing's gonna be on there for 15K.