the glitch is easy to use, or somewhat easy, when helping the asura to bring down the door if you can make it fail at 98-99 he will open the door to the endboss, without spawning his chest.
now go in and kill the endboss and get the chest, after that you go back and complete the quest before the endboss, and then you will be able to pick up the bosschest once more.
did it the first time by mistake and when i tried again it worked, though i cant do it with pugs as they go ahead and wont fail the quest at 98-99 as it should.
btw its explore mode