In the 3rd Edition rewrite of the famous module White Plume Mountain, the titular dungeon gets modified highly successfully to use 3rd Edition rules while staying very true to the original version in style. One specific encounter, however, sticks out as a very poor conversion...
Early on, the group is given a crossroads of three directions to choose from to tackle in any order. Almost immediately down one of these paths (canonically the "first" one you're expected to do, if the order it is written has anything to say about it), you encounter a slime trap. The rules state no way to avoid or defend yourself against this trap - simply that green slime falls from the ceiling when an adventurer passes below it, automatically hits them, and deals terrible damage (including Con Damage) continuously unless removed or burned promptly. It will immediately kill most typical adventurers in only a few rounds.
This particular trap offers no saving throw, opposed attack roll, use of trap-finding, or even a spot check. This is not the case for every single other element of the dungeon, which is full of Reflex-Save or Attack roll traps and ambushes that are all labeled and given statistics.
What happened here? Why is this trap so special and hardcore - and one of the very first ones in the dungeon, no less? Reviewing the 2nd Edition version, the trap was similar there (just even more likely to instant kill, what with Save vs Death), but all the other traps were similarly more hardcore, and were revised appropriately in 3rd Edition.
The rules for Green Slime are actually not unique to this dungeon, and are available at the SRD under Dungeons. It says that they hit a 5-foot square and deal their damage and effect there, but no rules are given for any kind of defense. This seems to be a major contradiction in mechanics and style to everything else in 3rd Edition.
Alternatively, are there any fair house rules for this situation? A reasonable spot check difficulty or reflex save ruling for how to avoid this slime?
Clarification: The major facet of the question is the inconsistency of the rules between this trap and all others in the module. 2nd Edition situations are well known for their difficulty, and 3rd Edition for toning down that same difficulty. The fact that this one type of obstacle is the only one that seems effectively "unconverted" in nature is what is being called into question.