I've got to Steel Mill and found something new for you to play with. Well, actually, not that new since it's already been reported once.
Remember that post by Jolteon where he complained about some underwater doors malfunctioning in level 8? Now I took the liberty to run some further tests on this subject. It turns out that one of the blue 2-part sliding underwater doors (SE 15 sprites 1229 and 1230) for some reason stops opening after the player opens a specific orange underwater door (SE 15 sprites 1353 and 1358). The latter one has a switch which makes it available for only 1-time opening. Seems that opening that orange door (one time, since no more opening sequences can be executed) is the exact culprit of the blue door starting to malfunction. Passing through any of the sectors beyond it doesn't seem to cause this.
On a side note, I think you should put something like a table with an instruction that the switch allows to open the orange door only 1 time (like you always do next to anything that "malfunctions", for example, a multiswitch code in the same level). It can be confusing to players without such knowlegde.
Also, there's a red door (SE 15 sprites 1274 and 1277) near the blue door in question. Jolteon also complained about it not opening in case you've hit its switch multiple times. I'd suggest that you put an instruction next to that switch as well.
Now I'd like to ask a question about a certain pair of doors at the same level. My investigation has proved there're two ways to get into that big hub area with 2 energy transformers (or whatever they are, they look like 2 energy beams with energy bulbs running along them) in the middle. Those ways are the doors with Activator sprite numbers 5733 and 5734 (look into the attachments #1 and 2 respectively to recognise them better). Looking into Mapster or even noclipping right to that area shows that initially (upon loading the level) the door 5733 is open (while 5734 is closed). It contains 2 corridors one above the other; the upper one contains a side compartment with an energy platform field and a set of buttons which open the red door (Activator sprite 6648; see the attachment #3) near the force field in the hub. The door 5734 contains a vertical obstacle room with instakill spikes, electric wires and energy platforms and ultimately leads into the aforementioned hub, ending up on the second floor from the top. The problem is, on my both playthroughs, as soon as I got to the said pair of doors, I'd always see the door 5734 open and not the other one. I'm curious as to how I'm supposed to get to the hub via the second path. Also, the door 6648 (the one that opens into the hub from the 5733 path), well, its Activator sprite, is linked to another sprite (to me it looks like a Touchplate effector) 8339 as well, but it doesn't seem to do anything. I'm theorizing the 5733 door is a delayed one (closes after some time since level start has passed), but ain't sure.
And the last thing: the self-repairing armor glitch (when it doesn't regenerate till finishing the level) is actually real and it seems to happen regardless of the armor type. But I'm not sure what causes it. Somehow it might be linked to using the claw underwater (maybe even with Pearl of Power in possession). If I ever discover the cause, I'll let you know.
P.S.: Whew, I hope the first two points don't inflict much confusion on you.