First off, the quest does NOT call them muckdwellers. he says the ones in theramore are called muckdwellers. the ones you are looking for are called slit crawlers and monstorous crawlers. the slit crawlers are level 40 and 41, the massive crawlers that i saw were all level 44. try not to go down to the southern shore area if you are alone, and don't have a pet, and happen to be under level 40. it's UNSAFE. there are dragonkin(40-45 elite), and murlocs(40-44), and spiders(40-41), and high level KOS humanoids(over 49) all about down there. unfortunatly, once i got down there, i was stuck down there, so i eventually suceeded. it took around 30-35 minutes at level 39 with my hunter, and the payoff was dismal compared to the effort to get to swamp of sorrows in the first place, and to trek across it(it appears almost all horde/KOS/dragonkin, so it's not kind to alliance folk. :-/&nbsp )
i would hold off soloing or partying it until level 41, for best results.

You have to go to from Dustwallow to the Eastern Kingdoms, Swamp of Sorrows. That's why he asks if you're "willing to travel", it's a far away quest. The coordinates in the previous posts both correspond to areas near islands, but the pristine legs come from monsters in the Swamp of Sorrows, NOT Dustwallow . So take the ship back to the Eastern Kingdoms, from Menethil > Iron Forge > Stormwind > Darkshire, then walk along the road going EAST, keeping to the path on the LEFT, walk THROUGH Deadwind pass to the other side, you'll come out on the west side of the Swamp of Sorrows, in order to complete the quest, you need to go to the other side of the area into the water, where, at the locations mentioned above, you'll find your slit crab dealies.

Go to Darkshire in Duskwood, take the road East out of town.

That leads to Deadwind Pass.

East across this zone leads to the Swamp of Sorrows.

easy to have this done under 5 min!

Whether it's easy to accomplish this quest, which as I remember from the last time one of my characters did it, involves gathering of the quest items on the east coast of the area and your recommendation is to come in from the west side of the area, depends entirely on one's level and abilities when attempting to navigate to the appropriate area to perform the requisite activities. If you are just finding out that you need to follow those directions to access the Swamp of Sorrows, you are probably unaware that Alliance players will almost immediately encounter Stoneard Scouts and Stonard Explorers, marked PVP, patrolling the paths on the west side of the Swamp of Sorrows. If you don't want to be flagged for PVP for fighting them, they need to be avoided. And that's just the first of your worries for taking this path to the quest area. The path soon branches into paths leading southeasterly and northeasterly. The southeasterly path will take you smack dab into Stonard. If you get too near it one or more level 65 Stonard Grunt (Bosses) will come out and attack and you'll be quickly dead. Again if you attempt to fight them, you'll be flagged for PVP (and dead). As soon as you spy it, detour to the northeast. The northeastern path leads into Fallow Sanctuary. which you'll also want to avoid as you'll get mobbed on your way through. So in either case you will be traveling off of the pathways and across country and likely agroing one battle after another with Swamp Jaguars, and Sorrow Spinners in the jungle, and Sawtooth Crocolisks, Snappers, and Tangled Horrors in the waterways. You may encounter the Pool of Tears in east central Swamp of Sorrows, which is generally quite safe to swim across the top, skirting the Temple of Atal' Hakkar in the center of the water. Once you reach the Misty Reed Strand, which forms the northeastern coast of the Swamp of Sorrows, be careful of the level 43 Monstrous Crawlers if you decide to attack them, as they can be problematic for lower level characters on this quest. So bottom line is if the quest is red or orange to you, tread very carefully when going this way. If it's green or gray to you, then it should be relatively easy to get across the area (and you probably already have the map filled in for this area, having been there before...).

You have to kill "silt crawlers" https://classicdb.ch/?npc=922
or "monsterous crawlers" https://classicdb.ch/?npc=1088
located along the eastern coast of Swamp of Sorrows.
I found the most around 95, 48 but they can be found anywhere along the water, they have a good drop rate.

Another interesing point for those who read the posts too quickly (like me) and miss that the 85,16 location is NOT in Dustwallow (where you get the quest):

That location in Dustwallow will put you just East of Alcaz Island.&nbsp Home to level 59-61 elite guardians of the imprisoned King Wyrnn of Stormwind.&nbsp Not good swimming water :-)

See this discussion as well.

Make sure to head over to the Swamp of Sorrows in the Eastern Kingdoms before locating 85,16.