My '75, '81 and '88 Hondas called for changes every 30K miles, and that’s what I did.
My '06 Toyota doesn’t call for a change unless towing, but it has the C59 transmission which has an iffy reputation regarding bearings, so I changed it early to assess the trans health.
At 21K miles it looked “dirtier” (with a metallic sheen) than the Honda’s oils did at 30K.
I’ll change it again after another 30K miles and extend the interval if it looks clean.
Cheap insurance.
Once you can get Honda manual transmission fluid the 10W-30 fluid should be changed in favor of the Honda brand fluid.
ALL manufacturers for the past 30+ years that I’ve seen have some type of writing like that in their manuals. Honda DOES NOT…and has NOT ever made transmission fluid (automatic or manual). It’s made for them by one of the trans fluid manufacturers. Same goes for every other manufacturer on the planet.
Just to add to the list; my manual transmission Ford Focus call for Ford Dual Clutch ATF.
2010 KIA Forte SX, 2.4L 6 speed manual 28,000 miles. I have had my vehicle serviced at a regional franchise since new because they tend to do a very good job. They use 2 technicians, 1 in the pit and 1 under the hood. They go back and forth calling out checklist items and receiving a response. there are 2 video cameras in the pit and 1 under the hood with 3 monitors next to the driver’s window so you can see them perform the checklist items. Of course they always try to sell a dozen different additives, windshield wipers, and air filters. I just inform them that I don’t use additives and am capable of inspecting and replacing wipers and air filters myself. No problem. About 2 weeks back I had my usual 5,000 mile service done at different location. Everything was normal including the pit tech performing a dip test to check the manual transaxle oil level smearing the oil on a white card and handing it to the topside tech for me to look at. As always it was perfectly clean. The service was completed and the topside tech handed me a flyer with 11 services that “needed” to be performed soon. He said most of them were not a crisis but the first one was way overdue which was drain and refill the transaxle every 12 months. I informed him that my car had a MANUAL transaxle! He replied that everything on the list was recommended by KIA. I told him I would have to check that out. When I got home I checked my owner’s manual. “Inspect manual transaxle fluid level at 40,000 miles or 48 months.” Since it has been inspected every 5,000 miles I think I am OK! The best part is when I read the “overdue” service on the flyer. It was titled AUTOMATIC TRANSMISSION/TRANSAXLE LINKAGE! Manufacturer’s Recommendation: lubricate every 12 Months. There was no recommendation for manual trans linkage. I find it sad that most of these young people have no idea what a manual transmission is. Most of the now vintage made in USA manual trans vehicles that I owned or serviced used good old stinky 90W gear oil. The British cars that I owned used 30W oil the same as their engine. My KIA uses API GL-4 (SAE 75W-85 fill for life) per the owner’s manual.
My 81 Horizon used ATF in the differential which had its own lubricant supply separate from the transmission.
At 70,000 the diff started to whine and I replaced it with 80-90 gear oil. No more whine and never any problem.