CSL 1973 said:
As regards engine oil, I will switch to Castrol Classic XL 20W 50. This mineral oil for classical cars, produced between 1960 and 1980, is recommended by BMW Mobile Tradition and is listed in their brochure. BMW sales the oil for 35 euro + tax (5 liters) and the BMW ref nr is 83210398771.
http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9014107&contentId=7027099#7094382
Cheers
For what its worth, Castrol passively suggests its synthetic may also be suitable for classic cars:
"Castrol Formula RS 10W-60
A fully synthetic engine oil that offers exceptional engine protection in performance driving conditions. Aids your engine in operating cleanly with reduced emissions and noise levels.
Not typically a Classic oil but recommended by Castrol as a replacement where a 20W-50 is preferred when you want the ultimate protection for you classic car"
Mobile traditions certainly offers conventional mineral oil "(Part number: 83 21 0 398 771 Supplement 5000ML Mobile Tradition Mineral oil-based multigrade engine oil
for engine technologies from The 1950s onwards with oil filters)." But I do not read this to mean BMW disapproves of the 10W-60 or that it would somehow void your 1950's extended warranty if you switched to synthetic. Is it really any different than if you decided to operate an old car on modern- unleaded fuel. And, what if my post 1950's car did not run an oil filter? Not good for the Isetta?:lol:
Who knows better? They are both well known brand names, presumably with empirical data behind their recommendations.
