Numerous sources around the internet list the pools in the Temple of Yak as being able to raise some stats permanently. Specifically, one gives +5 to Personality if that character's stat is under 21 (and also causes disease) and another gives +5 to Endurance if that character's stat is under 21 (and also causes drunk).

I'm trying to get to these pools as early as possible so that I can get those stats to 20 and then barrels will be able to raise them even higher. However, when I use the pools I don't gain any stats at all, even though the relevant stats are under 21. I just get drunk or diseased.

I'm wondering if there is something about the GOG release that patched out this benefit, or perhaps it only applied in Clouds of Xeen and the combined Worlds of Xeen no longer lets you do this.

I'd like someone else to confirm this if possible, or if I've done something wrong or don't realize the way this is meant to work, please let me know.

It's not too difficult to get to that area to check this out, though monsters may cause problems, and it requires 2 characters with the Pathfinder skill to walk through the woods. In Vertigo, visit the mirror and type Nightshadow to warp there, then turn around and exit the town. Go 2 steps south and 2 steps west to the tent, talk to the woman there to gain a key to the Temple of Yak. Then go 2 steps east and 1 step north, and 6 steps east to the temple. The two pools are essentially straight forward (east) from where you enter.

From the cluebook:
Yak Pools are available for bathing, if you are brave. Most of the pools will reward one of your characters for bathing in it, but a second bath will only rack up more penalties. Bathe at your own risk!

Yeah, I know several resources say these pools provide rewards, but I can't get it to happen in practice.

From looking around a bit, there's even a thread here at GOG that mentions the same thing, that bathing should give you stat increases if they're less than 21. I can't post links yet, but it's the last post in the thread titled "what happened to his endurance."

My stats don't change though, they simply get worse due to drunkenness or disease. When I click on the relevant stats, they don't show a different maximum.

Well, I think I've solved this on my own.

I started watching someone play the game on Youtube as I played it, just for kicks, and he got to the Yak temple...turns out I was using the wrong pools all along. The stat boosting ones are in the southern part of the map, south of the ones I was trying to use. Whoops!