The Vile Reef, where this quest takes place, is the location of several quests. It is a good idea to do all of these quests at once. As of patch 2.3, area is no longer elite.
The murlocs are located off the west coast of northern Stranglethorn Vale, almost directly west of Grom'gol Base Camp. The Saltscale murlocs drop the fins, and are located deep underwater. An underwater breathing potion (craftable by players with the alchemy profession or found in the Auction House) could be very useful for this and other Vile Reef quests.
Our rocket car is the fastest thing on the flats! So fast that ... I'm afraid friction is going to tear it apart!
To prevent that I need to create a composite to coat the car's moving parts. It must be hard but not brittle, and must be resistant to salt corrosion, or time spent on the Shimmering Flats will eat it away.
Have you heard of the Vile Reef, <name>? It's off the coast of Stranglethorn Vale. Saltscale murlocs live there, and their tail fins are a crucial ingredient of my composite.
Reward
You will receive:
75
Progress
Do you have the tail fins? If I can't protect our car from its own speed, then it won't last long in these races.
Completion
Thank you, <name>! After I grind these down and fuse them with a few other ingredients, the composite will be ready. And after that, the car will be safe from its own speed.