Well, my habit of buying new containers of oil at car boot sales is going to pay off. i find a lot of 1 litre containers that are supplied in new cars and these often find there way to the boot sale. I find that new cars i have had in the last 25 years have never needed top up between services.
I have quite a large collection of Mobil 1 motorcycle oil bought at 3 pound a litre for my new bikes but i bought a bit too much being a bit greedy. Now i only have 1 modern bike