I'm trying to understand what you mean by this. If you've an issue with a quest that has saved itself over 300 hours, you may not have the ability to correct the issue.
When you don't get a quest marker, that's an indication your target no longer exists. Shockingly, it can even happen while you're on your way to a quest. I remember going after a Raider settlement only to arrive moments too late as a Deathclaw took them out. It was the first time I ever saw a quest marker disappear from my compass map while I was there. Pretty incredible, actually.
Here's something you can try. Head back to Sanctuary (just to be safe) and find a chair. Then:
-Find a seat and wait 24 hours.
-Get up, walk about a minute, then save the game.
-Repeat these steps 2 more times.
This forces the game's "3 day cycle" reset (walking between waits prevents the game from crashing doing consecutive saves). Then, make your way back to WH. The quest should have failed by now and you should be set to get another.
The target should be different than the drug den. Rarely does the game resend a player to the same area twice unless the area is scripted. If you don't receive a quest marker this time, then I'd say you definitely have a glitch that's followed you over all these saves and hours.
Not sure what could be done at this point to fix it, so the only thing I could say is to ignore it, svcky as that is.