The factory filled M47 gearbox oil is a colour-less, odour-less, synthetic lifetime oil that should never be changed.
This oil is no longer available, it isn't made anymore and the superseded replacement isn't the same and is not as good. The owner's manual says Type F ATF, which of course isn't what the factory filled fluid was. I have witnessed myself (and others) inspect the fluid on 240's with M47 with over 200,000 kilometres and being 25 years old which I have known to never have had a gearbox oil change, and the fluid was still clear, no colour and no odour at all which at the time Volvo knew what they were doing when they said it was a lifetime fluid. Why the owner's manual does not say this remains a mystery to me.
I do not know why, but there is something in the guts of an M47 that is very oil-type sensitive and the wrong fluid can destroy one, whether it's the material of the synchro rings or something else.
I have heard the Fuchs Syntofluid gear oil is the equivalent, so now that your original unicorn fluid has gone, try the Fuchs. I have heard Redline MTL to be long lasting also.
Another thing with the M47, is to overfill the fluid by raising the left side of the vehicle. In the later M47's, named M47II, this is not necessary as the factory moved the fill plug higher up on the casing so as to allow more fluid in. If you don't, the 5th gear assembly runs dry and this leads to premature wear.
