VW Quantum Blue Mineral 15W/40 if it's a petrol engine.....Quantum Red 15W/40 if it's a diesel.
10W/40 is generally too thin and may cause hydraulic tappet rattle on wasserboxer (petrol engined) T3's
Both are shown here:
Of cause any decent quality 15W/40 will be fine.....but as our vehicles get older and oils generally become thinner, it becomes increasing difficult to find this viscosity (thickness) of oil....Halfords sell one, GSF do FUCHS, THE RANGE strangly sell UNIPART OIL in this viscosity,,,all of which would be fine...but as I say...Diesel specific oil if you have a diesel engine.
Martin