?I picked up one of those miscellaneous "kill the leader of..." quests and have clearly have already gone there and cleared the particular Forsworn camp out.

Now when I got there the white quest marker is simply pointing to the ground outside a tent, presumably where I'd already killed the guy before taking this quest on. There is no body or anything but a sword is lying there.

Is there any way around this or does it join "Repairing The Phial" (due to the "Take a Forsworn Heart part) in being unfinishable?

I had tihs happen too. I found another briar heart and that seemed to be all that I needed.

I have a lot of quests like that... specially in Markarth/The Reach... where I have to kill someone that's already dead. The same thing happened with Collecting Bounty from Skald (The Jarl) in Dawnstar (2x) that I had already collected, but it won't clear from my misc quest list. And now in Winterhold where I have to kill a dragon that's already dead. Same thing with buying the house in Markarth.

I had already read the book 'The Legend of Red Eagle' more than once only to find more than 1 Red Eagle Sword (about 3) so I had to go through that quest 3 more times (eventhough Red Eagle was dead) and that cleared it, but I don't know how to clear the others.

These miscellaneous quests that are already completed, but the entry doesn't clear from the quest log, does anyone know how long it would take for these glitched quests to clear from the log? They are completed, it's just the entry doesn't update on the log and I searched the internet for an answer and couldn't find one.

Yeah, I have about 8 of these completed objectives in my journal. Unreal.

This happened to me with the first Companion quest, got sent to kill a mage in the watchtower outside Falkreath but I'd recentley killed him. Eventually after a while (several days of ingame time) the quest automatically completed itself and I could get a new quest from Farkas

I have a few quests like this as well. One is an animal extermination quests that leads me to a dead animal. I also have a few collect bounties for said quests that wont trigger. I assume those are because the Jarls are stuck in Windhelm in the castle with no dialog options since they are under some sort of house arrest from the civil war.