Healing the plague - the game plot had only 2 potions, so the quest is supposed to stay as unsolved in your quest book. Therefore no XP? there are workarounds to still heal all - but no XP.

This quest does not expire, no time limit.

Breastplate: Did you once use the sentence "Let's forget it"? This seems to be a killer sentence and no breastplate dialogue appears.

http://kiya1.via.t-online.de/images/Divexp_Dragonpatrick.jpg

the dialogue is in the link.

Just to make sure: You've got the clue from the Dwarven King, right? could you ask him again? And Grisha, the Dwarven smithy?
If nothing helps

Raze has the Dragon Armour as a download in his fix, click here
Kiya