there is some oil change advice, Stu, on the Wiki pages worth a look, dont think there is a branch of GSF Carparts near you,but you will prob find the stuff recommended on the wiki advice pages elsewhere
I heard recently that GSF are going to phase out Quantum and are stocking Fuchs exclusively in future. I understand VW will supply it in all their new vehicles from now on. So Quantum may cease to be. Fuchs do a standard mineral oil to the same spec. You can use a synth or semi synth but as the engine naturally loses oil by design (no seals on valve stems) its a waste of time also the seals are more suited to a thicker oil so you will leak more using a synth.
Fuchs do a good gear oil that some GSFs stock too.. it's a semi-synth transaxle oil to give an improved gear-change with full diff protection, 4 litre container (ideal size) and seems cheaper even than the SX75W/90 in most Motafaxes..
Will put up the correct name and spec. tomorrow, after I've checked they are definitely going to to stock it and that its really suitable for our transaxles..
Been using 20/50 in my 1900 DG for almost two years now and it runs sweetly.
Engine has covered over 89,000 miles and 15,000 of that on the 20/50. I started using the Halfords Classic oil, looks like the old Duckhams stuff, but now using any 20/50 I can find.