Engine Oil Choice for 3.9 EFI?

What recommendations for a 1990 Range Rover 3.9 EFI please? I've used Castrol Magnatec for years. Some say it's too sophisticated for the 3.9 lump. Some say Castrol XL 20w-50 is best. What do you say? Where in London can it be bought at a sensible price?

10-40 semi every 5k.

Synthetic/Semi Synthetic oil is a complete waste of money and of no improvement to the old V8 at all.
It was designed to run on multigrade mineral based oils, either 15-40 or 20-50 in a UK type climate.
All the marketing hype tends to get people thinking that putting these high spec oils in an engine will allow it to last a lifetime !!

An excellent mineral based oil for the Classic and P38, V8 is Valvoline but any reputable manufacturers equivalent will suffice.

The secret is in REGULAR Oil and filter changes, not buying "Fancy" oils which will do nothing for your V8.

Valuable information.
Thanks gents.
Roger

i found 20/50 far to noisy in my 1990 3.9 over the winter months and went back to 10w40 on which it seems far happier-its also whats recommended in the handbook