Ok - Clearing up the Black Truffle issues
Firstly - was a very old concept so yeah the sprite isn't my best work to date (hating the deep muscle lines in the neck and chest now 0-o). Neither is the text the best - TJ has every right to change the text if he doesn't like it, and set the rarity. So though it was part of my concept - it wasn't a given. Luck was he did keep both the text and the rarity status. When made we didn't have all that many rare dragons at the time.
As to the concept - yes they secrete oil - but it isn't great gooey copious amounts that drip from every pore in its body and stick to everything like Terpentines do. Someone mentioned rainbow boa snake skin - and in reality it is probably the closest to the actual concept. They rub the oil from a gland on their jawline (like a cat does) over their scales in a thin layer which dries into a waxy substance, protecting the scales from dirt and scratches and enhancing their normal iridescence - so yeah Luminas would find a kindred spirit. It is this super smoothness that makes them feel slick and oily - not a coating of thick goo. Once completely dried to wax the oil looses its pungency and therefore value as a perfume base. Only fresh liquid oil from the glands is good for this - and being near a lot of teeth - yeah it is safer for some low life poacher to kill it first and take what they can get - similar to what elephant and rhino poachers do today.Yes it uses more oil during breeding - and it gains that characteristic sweet musky earthy scent that people chase. So it is more valuable for perfume use at this time of year and why its so valuable. It does not 'wash off'.
As to who the dragon deems has a 'pure heart and selfless spirit' - your own thoughts and inclinations betray you in your comments - if you think it's selfish for a dragon to hold back what is its own property, you are probably a greedy person at heart and would shoot it if you met one and steal all you can lay your hands on because you deserve it. The oil and wax it dries into has other uses than just perfume (its polishing properties for instance would turn a basic leather armour into something only the wealthy nobles could afford, wood too treated with the oil would shine like metal), and yes can be sold or the products it makes sold making a poor man's life a little easier, and if you approach the dragon and actually ASK instead of TAKE - it is more likely to GIVE than to chew your butt off. Being a reasoning sentient Being, politeness goes a long way - as does fair trade or free gifts. Dragons love gifts.
Perhaps they should have been a super rare holiday dragon - since no one complained about the chocolates and their scent or rarity.
Either way - love em or hate em - they have been discovered in the backwaters of Galsreim after centuries of hiding from the greed of humanity, so they may be more prolific than we know.