Quest is "To Walk in Dark Places" it is the last part when you enter the vault you can click Torian Cadera over and over for rep with both mako or gault what ever is up only tested with gault as mako was maxed.
also it is the quest right before getting Torian Cadera
edit: also one of the ways to talk to him will give 75 rep each time other i think gives 25 and other gives 0
let me know how it works for yo gl