Not synth per se...but changing the oil before the additives wear out...in particular, before it becomes acidic and starts forming sludge.
Unfortunately, many oils will not make it 7,500 miles in this car before turning acidic. Most synthetics will make it that far...
2006 Corolla (kid's car - 108K, Conti Eco Contacts, Castrol Edge 5W30)
2005 MB S600 (63K, M1 0W40)
2002 V70-XC (165K, Nokian WR G2, Pennzoil Ultra 5W30)
2002 V70-T5 (143K, IPD bars, Bilsteins, Extreme Contact DWS, Mobil 1 5W40)
1992 MB 300E (Sportline - 123K, Nokian WR G2, Edge 5W40)
1990 4-Runner (V6, 4WD, mild lift - 239K, 31" BFG AT KO, Edge 10W30)
1932 Packard Sedan (straight 8, dual sidemount spares, original paint and interior, Shell Rotella 15W40)