for a long time now, i believe if you have old bikes,use old technology ...new bikes, then use new technology

 

^^^ This... As there is something about the Bushings in the 4-speed [either one, and Sportsters too] and Hypo gear oil... I use the same stuff I put in my Old Tractors gear box... No Problems.. But, I do Not have problems with the Dairy Queen/CowPie/ Maytag??, whatever ya wanna call it.. tho I do Prefer the Ratchet top [the Later One over the Early one]
I cartainly won't be pulling the tranny on my '84 over the Top!!!! Gotta know how they Work, and how to keep them Working!! Since the Shifting mechanism on the late [cowpie] is so Similar, the Ironhead guys seem to do Better with it in fact!! It is the Linkage that gives it a Bad Rap...

 

one of the manufacturers wrote an opinion years ago on GL-5 in HD trannies and recommended NOT to do it - here is an explanation taken from a long post on GL-4 and GL-5 - I think the question is whether or not the sacrificial coatings will form on the yellow metals in the 4 speed - no synchros - but there are bushing faces that experience some shock and I guess could be compromised

"Lets take a look at the API GL-5 rating. It is a rating for EP (Extreme Pressure) protection. The higher the EP protection, the higher the GL category. In normal operation, the sulfur/phosphorous additive forms a black sacrificial coating on the gears and anything it touches with a little pressure and temperature. As the gears turn, instead of wearing, the sacrificial coating of additives is pealed off or worn off. This is normal and acceptable in all steel gears. But when one or more of the surfaces is brass or another soft metal, the sacrificial coating is stronger than the base metal, and instead of just peeling off, it takes with it a few microns of brass that it is bound to.

A traditional GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the GL-5 product, so the bond is not as strong, and therefore can be peeled off without peeling a layer of brass (or less brass). This means that the GL-4 product provides a little less extreme pressure protection, so in the differential of a high-powered car, it would not be the ideal product in the differential.

When we use a GL-5 product in a transmission that requires GL-4, we normally find 2 to 4 times as much copper in the used oil as we would with a GL-4 product (with used oil analysis). Eventually the synchronizers wear to the point that they no longer make contact with the other half of the cone, bottoming out before stopping the opposing gear."

 

If you have an aftermarket matag mated to a 93" motor...you are a real gluten for punishment.