The quest "Revenge of Gann" obtained from "Gann Stonespire", requires you to destroy a "Bael Modan Flying Machine". Currently the Quest marker is a cog wheel that is at the keep Bael Modan proper, however the actual machine you must destroy is south west at the top of the archeological pit, on top of a wooden tower.

This is noted by the comments within the wow-head quest database, as well as attached screen shots.

wowhead link: https://classic.wowhead.com/quest=849/revenge-of-gann#comments
Quest Location Screenshots:

Cog wheel is shown at incorrect location. Player Arrow Icon is at correct location. (Coords: 47.0X, 85.6Y)

Hey @Zenatsu ,

I see you also have the Tear of the Moon quest -- that seems to be the gear on your minimap. It's located in the keep.

We seem to have the correct location for the flying machine in the data.

[3644] = {"Bael Modan Flying Machine",nil,nil,{[17]={{46.97,85.63},},},17,},

Sometimes objectives bug / disappear when you go into a dungeon and come back out, or play for a long time without reloading UI. Guessing that's what happened here.

Working on a fix for that in 7.0. (=

Cheers!