Gearbox Oil Choice? 2.3 T5 5 Speed

[Green440wedge]

The world of gearbox oils is quite confusing, it appears initially simple but it is not really. My V70 II T5 has done 113k miles and I figure the gearbox oil should be changed, I talked to an independent gearbox specialist who said at that mileage it would be a good idea despite the oil being designed for the life of the gearbox.

The Volvo spec oil is GL4 75W.
Comma do a GL4 75W and a GL4 75W80 fully synthetic.
Comma says their oils have not been tested on my specific gearbox though hence "refer to handbook", although their oils do meet other Volvo specs.

Carlube's old guidebook I found in a motor factors says 75W90 GL4 semi-synthetic. Their online system for my car says "refer to handbook" but if I put in a V70 I T5 or V70 II 2.4T then it gives 75W80 Driveline Multi-Vehicle Mineral Oil (this normally means a GL4 and GL5 compatible additive pack I think). I can't imagine the gearbox is different to mine....

The motor factors said 75W90 would be fine in an older higher mileage gearbox. Probably true.

I spoke to technical services at Comma and they said that EP (extra pressure) additives are now added to most gearbox oils, and that typrically there was more EP additives in GL5 compared to GL4. However, I think "EP" is also used as a brand name on GL4 products sometimes...

Anyway I have orded some "Made in Britain" Westway GL4 Synthetic 75W80, I got a good deal on it. I can't imagine it will do any harm.... I stayed clear of the GL5 which is not good for yellow metals apparently due to reaction with the higher dose EP additives. I just hope not being "EP" that it will be OK for the combined diff and gearbox unit.

If anyone has any better and precise expert level advice on this topic I would be interested to know. Thanks.