Wow! Who is this MokeTong guy that he can trash everybody and everything he sees as a threat to his kingdom as Lord Provost of the oilbob site? Let the OP clarify his question? No, call him rude for doing that, and begin nitpicking and demeaning the type of car referred to, and trying to rephrase the question so some tripe from a LucasOil website can be cut and pasted in as an answer, or something. How completely infantile. No people watching this site? Then (MokaTon) calls someone a Drunk Pot Smoker. This place is great, but no doubt I will get dismissed for even mentioning the content of the thread. If I last long enough I will post my somewhat related question in a new post.
The only useful piece of info that ever was brought up here, and related to the OPs questions, was about the buffering additives to keep an oil from becoming acidic too quick, so it can last between changes. Actually the OP did question about a possible lack of such buffers in even a good quality synchromesh (gear) oil, but I guess people were too busy trashing everybody else to have even noticed, and it just happened to come up again later, as if it had just been thought of. It was at least a step in the right direction, eh?
No doubt now I will be accused of being the sock puppet of the OP because I actually have read this entire discussion and am not a drunk dope smoker, so I actually can comprehend and remember what has been said. Nor am I some megalomaniacal drip with visions of oily grandeur who sees and knows all about everything oily, and apparently can do no wrong (except to other's) her on oilbob. Colorful IM's? Lucky you's. Keep your pants on (off?) and be happy you got what you were apparently trolling for. Yuk. I can swear as good as any Japanese Imperial Army soldier veteran of 1930's China plunder and pillage, if you would appreciate a sample to help you out there. It would be phonetically correct and it would be meaningless unless you speak Japanese, but still. Could be helpful to that person.
Quite frankly, I would have brought up Boron additive EP oil when the negative sulfur additives info came up. Boron is more common an additive for gear oils in Europe. Along with a sort of base level of sulfur. The Boron gear oils begin slightly more acidic than most all-sulfur ones, generally, but are quite well buffered against acidity. At least for gear oil use. Use in an engine, I just don't know? Would buffers be destroyed quicker there because why or why not? More heat in engine, more contamination, or what? Are you guys saying that typical gearbox oils with synchro additives are not buffered, or not buffered in the right way to be run in an engine? If that's the case, like about how long would you estimate (for laughs) it would stay buffered being used in an engine? I don't know, I am asking? I thought they would be buffered, and pretty much work wherever. Or are you guys saying just that the high sulfur ones are corrosive, by way of the high sulfur? An example of an EP boron sold in the US would be Delo Gear ESI by Chevron. Or maybe its Standard Oil Chevron, or Standard Oil of CA?
https://cglapps.chevron.com/msdspds/PDSDetailPage.aspx?docDataId=76979&docFormat=PDF Comes in a multi-weight 85/90 and 85/140. I am not saying this is any good for a synchro gearbox or to run in an engine, I am just saying it is a formulation that has some sulfur, but it appears to have boron instead of huge amounts of sulfur to achieve EP. The copper strip tests on this oil appear to show a very non corrosive (yellow metals) product. Not as non corrosive as the Redline MT90, but quite close and quite low on that tarnish scale. Something that may be of interest to cars like OP mentioned with yellow metal in differential and gearbox anyway. Not to mention the standard Delo 85w90 gear oil close to same viscosity as 20w50. And once again I am not saying to run it in the engine, just that there are some things to look at.
At least one other person on this topic has expressed interest in the subject matter of the question, and is not here for just the sideshow. I don't have an answer to the OP question, just some other possibly related info to add.
As this site was mentioned on a British car forum recently you can expect some traffic from there. I think it is pretty strange that at least one here finds trashing the car related to the question is somehow constructive. Is that your way of saying you have no answer because you cannot google it, so pick a fight and maybe nobody will notice you have no answer? Maybe you are still sour at having the RAF alone kicking the Luftwaffe into the dirt? This is not a discussion of the Lucas based fuel injection the Luftwaffe used to lose to the carbureted high octane RAF. It is not about you feeling poor self esteem over having the relatively primitive Mk1 Hurricane rule the sky's as early as the BOB, so you feel the need to trash all things British. Come out of your underground bunker some time and feel the sunshine. You might notice the rest of the world has moved on. The British car people know all about zddp levels, and discussion of zddp tends to inspire suggestions to go search archives, it is that boring to them on those sites. This site does have a good search feature that yields mostly relevant answers, given the right search terms. Better than most. So what would boron EP do in an engine is my addition to the topic here?