it is true morphine is very helpful but those other things missing from your games sounds so weird. I guess 1 option is to reset you cache but id only do that as a last resort maybe if you have access to another xbox from a friend or something to test it out.
Those guys in the sewers really piss me off. The flame thrower guys are such a pain in the ass to kill and normally can cook you from half way across the room while your hiding behind a pillar which is really irritating. I just used the lugar but if i ever make it there with morphine id sure use it to kill as that section can be a real pain.