My car isn't a Lumina, but it is a 1998 Malibu with the same engine. I
bought the car for $1500 and at that time, it had 249,000 kms. Since then
(9 months ago) I have put ~750 kms a week on it and engine wise, it has been
running trouble free. When you first start it, you hear the piston slap for
about 3-4 minutes, after that it goes away and is not noticeable.
My opinion; if this engine were going to break because of this piston slap,
it surely would have done it a long time ago when it had much less kms.