I use M1 5w-50 in my 90. It has higher zddp than many current oils, cf rated and is bmw high performance diesel approved. Mobil's tech help, once I finally got past the marketing types, said it was good for the application.
Roller lifters shouldn't have the problems that "flat" tappets do with reduced additives in some modern oils, but i prefer heavier weight, higher additive oils in my older vehicles.
'85 90 2.5NA
'72 SIII 88"
Couple other cars