You could put any gear oil you want in there that says "gear oil, so long as it's NOT suited for a limited slip differential. You might even do very well with automatic transmission fluid that was in the now dated Mercon/Dex2/Dex3 range, but that depends on the pumping/distribution system, which gets kinda sciency. That stuf at 10W (crankcase, not gearcase) keeps gears apart at 500 plus horsepowers and 1800 pounds...... It's crazy. You don't "need" the "thick" anymore.
If you wanted to be "right", the 140 is "probably" not "at" your favorite auto parts store, but I'd bet they could have it next day. And if there's any confusion in the ratings, GL1 is obsolete and probably off spec if it claims that, 2 is probably fine but most likely (no guarantee, most likely) has some "very short life" components that would need once a year changing if you never turned on the lathe, and three through five are very recommendable. And I fully assume that there's at least some yellow metal bits in there. The yellow metal issue is almost dead, (gambling is safeish, but not guaranteed) but if you're unsure, go to the website for a particilar oil you like, find the PDS (Product Data Sheet). This is an easy one. Either this sheet is on the website for the oil brand, or the oil brand is produced to be heavily discounted, and isn't necessarily the same from one batch to the next... Look for the copper strip test. 1A and 1B are what you want. Unlike most of this chemical soup that is modern lubricants, it's an easy one-liner. A does nothing to yellow bits and that's ideal. B might stain your yellow bits but it stops there, no corrosion, so no reall loss since you can't see 'em. But if it had gear oil from the 70s or 60s in it, don't worry, it's already stained, and it won't get worse. So 1A or 1B, same/same. Contrary to the internet's wistom, MT1 has NOTHING to do with yellow metals. I don't care how much "research" anybody did or how many people jumped on the bandwagon, the SAE papers that define the spec, are kinda what defines the spec, and it's clearly not that......
So, Recommendaton 1= Get the 140 just for the warm fuzzy feeling.
Recommendation 2- Get 85-90. It'll do everything the original did and ten times more.
