Ambassador Dvinn in crush not dropping black heart
 

This is for the gatorsmash maul. Pre-kunark he dropped it 100% of the time. I did the quest at least 50x. Since Kunark or a patch since then, he has no dropped it the three times I've killed him.

Of course not definitive proof but sites such as magelo and eqemulator show drop rates based on the live servers and they show it dropping 100%.

Its about a 50% drop, same as magelo etc.

https://eq.magelo.com/npc/19482

Interesting. At some point it changed because I did at least 50 of them pre-kunark and he had it every single time. Now post, 0 for 3. I can buy it's 50% now but it changed.

This shows 100%.
http://mqemulator.net/npc.php?id=58059&view=droptables