MG T-ABC

I see the TC requires a SAE 140 wt gear oil. I've had tremendous luck using Redline Shockproof gear oil in my other cars where it made a marked difference in the shifting and wear (or lack thereof). I'm curious if anyone has tried the Redline 75-140NS Gear Oil or is the multi weight asking for trouble?

I've heard of people using it with success but haven't tried it myself. I still use regular old SAE140 (GL4/5) from Napa.

Multigrade oils were not available when lubricants were being specified for the Tabcs, so the fact that they were not recommended does not mean they are unsuitable. I believe any additives should enhance the oil to a GL4 level
to give the EP (extreme pressure) protection needed for the Spiral Bevel differential gears. The gearbox also benefits from an EP type oil, so the GL4 rated oil was made common to both. Look for the GL4 spec. on the label.

My understanding is a bit different: 1) nobody as far as I know has anything against multigrades, 2) -EP spec is required for hypoid rear axles, where the axes are offset so there must be sliding contact between opposing teeth, 3) the strange smelling additives give this extra protection for sliding contact, 4) with spiral bevel axles and only rolling contact, we don't need this extra protection. I have read somewhere that the brass cage in the nose pinion bearing (the expensive double-row one) can be attacked by the nasty Extreme-Pressure additives. So I don't put EP anything in the axle or gearbox.
But I am not a tribology expert......
After teething troubles in 1989 after standing for many years, I have had no problems with the whole driveline since then, and TC2626 is USED.
Richard TC2626 in Germany

I cannot see the point of using anything but what the manufacturer recommends if it's still available, especially when expensive and hard to find parts are concerned.

Using anything else will invalidate the warranty.

EP spec. oils are required for spiral bevel gears due to the high tooth contact pressure which causes cold welding of the teeth surfaces. A sulphur based compound is added which produces an iron-sulphate coating, and prevents
micro-welding of the surfaces. The Tabcs spiral bevel gears were originally meant to run on Hi-Press 140 which had mild levels of additives equivalent to GL4. The term Hi-Press was absorbed into the general term EP and any distinction between spiral bevel and hypoid gears was covered by the GL4 or GL5 codes. To sum up, use EP140 oil to GL4 spec for the diff. and gearbox, the levels of additives will not harm alloys with zinc. To prolong the front pinion bearing's life change to tapered roller bearings as the original bearings were too close to their limits.

Although from what I understand, most GL5 oils today do not harm bronze and other soft / yellow metals. Should be marked as safe on the container.