In the slimes and oozes post, I didn't say all that much about slimes, other than they are more like non-mobile traps or hazards than actual monsters. In fact, Monsters & Treasure specifically uses the phrase "non-mobile hazard". They have hit points mostly to determine if the adventurers can cleanse an area; they do not attack, however. They seem to exist in OD&D primarily as "something the cleric's Cure Disease spell is good for."
I think the basic Green Slime kills a little too quickly -- no figure given for the LBBs, but 1-4 rounds for the Monster Manual. I'd prefer to use the disease rules I posted previously, defining Green Slime as a very fast spreading fatal flesh-eating parasite: infestation is automatic on contact, beginning at the incubation level ("UGH! What's on my hand?") and requiring a Con save every turn to avoid progressing to the next stage (severe, then fatal.)* Thus, Green Slime can kill in as little as four turns, but may move slower in healthier individuals.
*(This may be a good general rule for parasites: unlike diseases, parasites don't get better on their own, but must be removed, purged with a potion or herbal remedy, or killed. Spreading parasites will infest the whole body, while other parasites just infest one organ.)
I'd also allow color variation in the same way as oozes: color determines camouflage ability and each color of slime is vulnerable to one specific ordinary substance like salt or alcohol. I would not link color to special abilities/resistances; variant slimes have two primary vulnerabilities (fire, cold, electricity, acid) and roll 2d6: if doubles are rolled and total is <7,>7 means an extra special effect (bursting bubbles act like a splash attack, odor is incapacitation, etc.)
Ear Seeker: I'd reduce this to a standard fatal ear/brain parasite, meaning it takes days to kill rather than hours, and there's warning (mild stage: "My ear hurts!") There would definitely need to be signs of insect damage to a wooden door, wall or container, as a warning. Note that my alternative to handling cantrips makes a little 1-point extermination cantrip useful to sterilize a small area before listening.
Keyhole Creature: a variant ear seeker; it's a fast crippling eye parasite that causes blindness rather than death. Infestation is caused by looking into small, dark holes, at which point the parasite jumps towards the victim's eye. Holding your ear near the hole instead lets you listen for tell-tale scratching sounds inside the hole.
Lung Rot: a fungus that lives on cloth and leather which releases spores if disturbed. The spores are a slow fatal lung parasite.