The rancor is missing/nowhere to be found.

I've got Mission in my party, I've been all over the sewers, watched many Youtube walkthroughs, and still no sign of the rancor. I see in all the videos that the correct path is through the door to the left of the "waterfall", but every time I go through it, I just end up at a dead end (and no sight of the severed arm either).

Just read a post that said it's a known bug for a few people, and a kotor "restoration" mod was suggested. I don't like to install 3rd party apps or mods. Is there another way to get the rancor to appear? Enjoying the game but if I can't find the rancor, is that a gamebreaker, and I'm out of luck...game over?

IMO not installing third-party mods for the KOTOR games (even the first one) is a mistake, as you're missing out on a fair few fixes, plus some additions (which I believe are optional from the installer for the KOTOR restoration mod).

Seriously, just grab the KOTOR restoration mod, run the installer, read carefully what each bit changes and just don't install those bits that sound a bit dodgy to you.

Come to think of it, I'm surprised you haven't encountered other game-breaking issues up to this point already - is this before or after the swoop racing on the first planet? That bit bugged out for me without mods - either during the cutscene, just after or if that worked then the race itself had issues. The mod fixed these.

Also, I'd recommend getting a HD resolution mod for KOTOR as well - that by itself actually goes a long way to fix certain other crashes, and is probably more important than the restoration mod.

I have encountered this problem before. IIRC I had missed a conversation that primes the trigger for the event, and I solved it by going back to speak to someone or other about something that fixed it. Or else I just reloaded an earlier game save. I haven't installed any mods for the first KotOR. either.

Parts of the restoration mod are "dodgy"? Really? Can I have some specifics? I've already installed it. Wonder if I should be concerned.

You'll see, it doesn't hide anything from you. Some of the stuff may be the makes of the mod going a bit far in terms of "restoration", e.g. they restore something that was cut for good reason. These are all subjective of course, which is why they give you the choice. In other cases they may be OP.

There's also a MASSIVE restored portion, which is a Pazaak tournament, kind of done World Series of Poker Style. I'm not sure how much of that was actually already there and how much of it was just some modders putting a lot of effort in, but I personally enjoyed it - even if it does mean you end up with way more cash than you should (but the game's not exactly difficult anyway, so you may as well have fun and get the best stuff).

Actually while writing this something came to mind, but I could be mistaking it for a different addon mod - basically this added some stupidly easy boring stuff in one previously-empty level, which nets you stupidly OP stuff.

Personally I didn't find any of the "restored" content in the first game anywhere near as dodgy as some of that restored by the kickass restoration mod for the second one - luckily there are mods to disable various parts of that mod. They definitely went a tiny bit overboard with that one.

But if you didn't get the options on install then maybe you installed something different? Or I'm just misremembering? Anyway,. you should be fine - and if not there are always more mods! :)