[SBTork]

I ran valvoline durablend (synthetic blend) in my '86 for a few years then switched to Valvoline fully synthetic, then gave royal purple a try. For my money, i'd go back to durablend or valvoline fully synthetic. I did not have any problems with royal purple, im just not convinced it's worth $8/quart.
That and a good PF35L, high effiency ac delco filter or a K&N performance gold oil filter.