Bulldog, you sound like you aren't a huge fan of the Yanmar machines....
I agree with you on proper maintenance being both time consuming and not cheap, and that going lower quality isn't necessarily saving money.
I have no experience with the Costco fluid, and have never had hydraulic fluid be a problem with any machine I've ever had, except when it leaks out.
For that matter, I've only had one machine ever fail because of a lubrication issue. When my brother was 12, he borrowed a 2 stroke dirt bike, filled it straight gas, and took it for a ride. He made it about 13 miles before the engine seized.
For my dollar, doing the maintenance is more important than what you use, as long as it's a compatible product. For example, Wal-Mart Supertech 15W40 oil comes out as being better than some name-brand products (Like Delo 400 LE, Rotella T Triple Protection, Amsoil Synthetic, and Castrol Tection), largely because of the CI-4 API specification rather than being a CJ-4 oil. I attached the test.
I have a lot of equipment that sits for sometimes 2 years before I ever even use it (Post-hole digger, manure spreader, etc.) I don't see any reason to run expensive fully synthetic oil in the gearbox of a post-hole digger that hasn't been under power for an entire hour over the 10 years I have owned it. I change the oil before I'm going to use it: Literally every couple years or so. For that machine, my best maintenance tool is a tarp, to keep it covered. Consequently, when it's time to service the gearbox of that thing, I run Super-tech oil, since it is the cheapest, and isn't an inferior product.
In a machine that does a lot of work with its hydraulic fluid, I see the benefit of running fully synthetic fluid, with top specifications. Loaders, hydrostatic transmissions, and hydraulically powered implements will logically be tougher on the fluid, and more demanding. The expense of the product is counteracted by the improved service intervals. In a gear tractor, that uses the hydraulics to lift the three point at the end of a row, I don't see what benefit the "better" product would be.
The machines of 70 or 80 years ago are doing that same work, and probably some are a fluid change of 40 years ago, maybe more. The guys with the 8Ns don't fret about the hydraulic fluid-they're too busy working on the ignition systems. Lifting an implement, then lowering it for a few minutes, then lifting it again isn't going to be tough on fluid.
The original poster's tractor, as Pat331 pointed out, has been in a flood. It will probably run and work ok without changing the fluid, but he should. The Costco stuff, as long as it meets some reasonable specification (JD303, IH Hy-tran, or whatever) will be great for your machine. Use it for awhile, then change it out again once it's milky.
Buy the cheap stuff, Gurn, and use the money you've saved to do more frequent maintenance and buy parts until you've got the bugs all worked out. I think doing maintenance is more important than having expensive consumables.
The savings of the Costco fluid over the other stuff will let you do a whole flush of the system and fill it up again. That's better than running contaminated synthetic stuff at 90 dollars a bucket! I'd do the same thing with the engine oil. Good luck with your resurrection of this drowned Kubota!
