Volvo Repair: 2002 S40, 1.9 turbo, decent cars, safe car

Question
This fully loaded used car is selling for $9,000.  The interior and exterior are in great condition, but we suspect that the oil hasn't been changed in 15,000 miles and there is sludge upon opening the oil cap.  Also, the air-bag light is staying on, and we heard a slight whistle while test driving.  We have never bought a used car before, and we want a safe car for our teenaged son.  Would you purchase this one?

Answer
Michele, those are decent cars.  You would need to do about 3 oil changes to get rid of the sludge.  1 oil change per 1000 miles.  Other than that an engine flush service would remove that.  As far as the bag, that would have to be scanned to see what the problem is.  Roger