Castrol GTX 20W-50, which many of us have been using for years, now says Classic High Zinc Content on the label. If this is a change in formulation or just labeling I do not know.
Bill Husted
Barre, MA USA
1963 R60/2 w/ 1955 Steib S500
1973 R75/5
In the engine of my R75/5, I run Valvoline fully synthetic 20W50 in the summer months and switch to 10W40 in the winter. I drain the oil in November or December but don't change the filter. In late March or April I put in a new filter with the new summer oil.
In the gearbox, drive shaft and final drive I run Valvoline fully synthetic 75W90.