I'm betting that Hydrophane is just a more refined animal-based oil. Probably has some other stuff in it, too, but I bet part is good old neatsfoot. It is a bit lighter oil, though, so there's more to it. Probably the unicorn chins. Or processed olives.
Oh, yeah, the mold thing. I was raised in sunny CA, in the dark ages when new leather was dryer, and rode mostly western anyway (thicker, less refined leather). Or old Stubben saddles. Went through neatsfoot like crazy. It's taken me several years, living in the humid south, to adapt my leather care to get throught the cold winters but not disappear in a grey cloud in July and August. Still isn't ever foolproof.
"One person's cowboy is another person's blooming idiot" -- katarine
Lexol conditioner and glycerine is a staple for me for dry tack (useable for every day after cleaning, too).
I don't like greasy, sticky beeswax products like lederbalsam. The leather may feel nice and supple, but it attracts dirt like a magnet and creates a gunky buildup over time. It's not so bad to use on your saddle before going xc, it provides good grip and waterproofing; but I've learned for every day use, a "lighter" oil product that completely absorbs (or evaporates) is a better alternative.
“A clever person solves a problem. A wise person avoids it.”
? Albert Einstein
The thing I find most interesting about tack cleaning and oiling is that everyone swears by different products and almost everyones tack turns out just fine. I've handled bridles that are cleaned religiously with saddle soap after every ride and I've handled bridles that are wiped down and lightly conditioned with a conditioning balm only as needed. I couldn't tell the difference.
I do think that some saddles start out "thirsty" and I do not think you are going to ruin the stitching if you go to town with hydroplane, neatsfoot oil, olive oil, etc. My saddle is at least 15 years old and it gets drowned in oil a few times a year. The leather is supple, stitching is tight, and I see no reason why it won't be usable for another 15 years.
The moral of the story is that the OP needs to post pictures, or some Professional Leather Feeder needs to come over for an intervention.
IMO, a saddle that has been oiled decently at least once shouldn't squeak. I have met (and fed) some Pessoa saddles that were permanently thirsty. But that's unusual.
IMO, you can feel an oil's thirst-quenching properties. The heavier, thicker it feels, the more it satisfies the inside of the leather.
I like pure neatsfoot, but I see how olive oil could be good, too. Hydropane seemed too thin to me. You got the oily shininess on the outside but when you bent the leather later, you didn't get the same suppleness.
It's not the tree. It's mild squeaking where the stirrup leathers rub against the flaps. Goes away with oil. Has come back after generous oiling #1. The saddle hasn't been ridden in 25 times yet. I do think it's simply thirsty.