I just purchased a 2004 S80 with 24K miles. Should I use sythnetic oil? Is thier any downside (except price)? I want the car to last a long time. Also, I am told that the oil--any kind- does not need to be changed until 7500 miles. Is it wise to go that long?

I just purchased a used 2004 S80. I absolutely love the car, with the exception of the radio. It has a dated casette player and it is not easy to find stations quickly b/c it has no buttons, just a dial. Does anyone know if there is a different Volvo radio for the 2004 S80. Any ideas? Thanks so much!