Thanks Bill, but the Shop4Parts link above to Tutela is GL5 spec,
https://extranetpli-eu.pli-petronas.com/dsp/pdf/eng/scat/1475_scat_eng.pdf but my handbook says I need GL4
I understand getting the wrong GL can cause damage too. Pretty complicated stuff, oil! The Morris is GL4.
Almost anything mechanical, and especially if it's to do with IC engines, interests me but I've always had a special interest in tyres (I suppose due to my earlier employment) and over the last decade I've become more and more interested in lubricants. So I'm always looking for info and articles on that subject. Opie Oils is a highly respected supplier/specialist and they have this article on their website which you might like to read:
https://www.opieoils.co.uk/t-api-car-gear-oil-specifications-explained.aspx Right at the bottom there is a small reference to the GL4 vs GL5 problem.
Some years ago, when GL5 first appeared on the scene, there were reports of it causing damage to the soft metals, some call them "yellow" metals, in gearboxes (so brass and phosphor bronze typically used in bushings and synchro rings). I've read a lot about the problem and if you want to go into it in much greater detail without getting too ridiculously technical this article explains it all quite eloquently:
https://www.widman.biz/uploads/Transaxle_oil.pdf Although it refers to the Corvair (a vehicle which interests me greatly which is how I came across it) the problem caused by the oil would be applicable to any vehicle.
Today though there are anomalies. Some (possibly many) of the manufacturers claim their GL5 is now completely compatible with older boxes which needed GL4 but I've been unable to find anything definitive as to why and then there is a "rogue" spec, not quoted in any official API list I've seen, of API GL4+
In fact the Tutella Technyx
https://www.shop4parts.co.uk/?name=..._Panda_III_(09_to_12)_1.2_8v_Transmission_Oil which I use in my Panda and my boy's Punto is rated GL4+ So, personally, I always use the actual oil recommended by the manufacturer. I think if you go by Shop4parts recommendation for your vehicle you won't go far wrong and if you're feeling unsure please do just give them a ring. They are very helpful and approachable people (who all seem to be called Mike or Mick!) I've rung them a few times to sort something out which wasn't listed on their website - they seem to stock, or are able to get, a lot more than they list on line - and they've always been extremely anxious to help.
Finally though I would say, that unless I had very strong evidence to the contrary, I would not be putting a GL5 oil in a box for which the manufacturer's original recommendation was for a GL4. - But then I'm a confirmed "feardie"!