I think it would be wise to switch to synthetic. I don't know if the oil they put in was synthetic or not. Since on a 99 you would be responsible to pay for all the maintenance yourself, you can tell if it's synthetic by the price. The non-synthetic at most dealerships would run in the neighborhood of $2 a quart, the synthetic would probably be 6 bucks a quart, and the engine should have had 8 1/2 quarts put in. At our dealership, the oil is in bulk, both the synthetic and non-synthetic, so we can charge out a 1/2 quart, your dealership may have charged you 8, 8 1/2, or 9, depending on their own capabilities. So, if it's synthetic, you would have paid roughly $40 to $55 for the oil alone, or if it wasn't synthetic, it'd be more like $16 to $18. I'd recommend the Mobil1 0W-40 if you can find it. Also on the oil, if the price is confusingly in the middle of the range I speculated, just call the dealer and ask what type of oil the Castrol is that they put in.....Gilly