My '67 R69S had detergent oil from 1967 until about four years ago (first Valvoline, then Shell, then Castrol). The slingers were cleaned at around 60,000 with no signs of impending failure at that time. Since that service it has had Amsoil synthetic. It is about to turn 80,000 miles. May blow up any minute now.
Jon Miller
'67 R69S
'13 F800GT
Altadena, California