In my last service for the little Laser 1.6 I used up leftovers from three different brands of 15w40 oil, including about 600ml of Penrite as well as 500ml of 20w50 I had stored in a small power steer fluid bottle!
I did this to save the remaining 4 liters of Penrite for the V8 Fairlane's next oil change and hold out for the next sale.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!