As was mentioned in the previous post, Marlow is more fascinated with meeting the man behind so many rumors in order to see how living in the heart of the Congo has affected him. Throughout Marlow's journey to the Congo, he learns that Kurtz is the most successful ivory trader and many selfish individuals wish to see him dead. Marlow is also familiar with Kurtz's earlier goals of bringing the "light" of civilization to the Congo, and he wishes to see if he still maintains his beliefs. Kurtz's enigmatic nature fascinates Marlow, who is utterly disgusted with how other Europeans in the Company conduct themselves. In a way, Marlow is motivated to meet Kurtz in hopes of finding a European who is pure, morally upright, and successful. Upon reaching the Inner Station, Marlow discovers that Kurtz has been utterly corrupted by greed and uses his status to wreak havoc on the surrounding African villages. However, Kurtz does not attempt to hide his depravity and immoral actions like many Europeans associated with the ivory trade.
I suppose really Marlow doesn't "want" anything concrete from Kurtz. He associates Kurtz with the irresistable attraction of the un-mapped central parts of Africa, and as he discovers more about Kurtz, he feels an association with him that grows throughout the rest of the novella. Not only are they linked by their common European heritage, but also Marlow becomes fascinated by Kurtz's story and his ideals concerning colonialism.
By the end of the story, however, Marlow has discovered than another link binds them together - the infinite corruptability of mankind, no matter how noble their intentions are. Kurtz's final words ("The horror! The horror!") can be said to represent a judgement on humanity and our ability to be corrupted without the restrictions of society to keep us in check.