I remember once many years ago reading a short story about how the Human Race established contact with an alien race. One of the exchanges involved one alien and one human meeting in orbit on a space station for the purpose of collecting what the alien would extrude from it's pores. This "elixir" would extend life expectancy in a human who ingested it. The problem arose that the alien was so "foreign" and grotesque that if one was to "view" it, one would go mad. This story is a narrative of the man sent to the station for the collection and his encounter with the alien.
I believe you're referring to the short story "Stranger Station" by Damon Knight. Short excerpt:
Deep in the vats, the golden liquid was trickling down: “Though disgusted, I took a sample of the exudate, and it was forwarded for analysis…”
Space-cold fluid, trickling down the bitter walls of the tubes, forming little pools in the cups of darkness; goldenly agleam there, half alive. The golden elixir. One drop of the concentrate would arrest aging for twenty years—keep your arteries soft, tonus good, eyes clear, hair pigmented, brain alert.
That was what the tests of Pigeon’s sample had showed. That was the reason for the whole crazy history of the “alien trading post”—first a hut on Titan, then later, when people understood more about the problem, Stranger Station.
Once every twenty years, an alien would come down out of Somewhere, and sit in the tiny cage we had made for him, and make us rich beyond our dreams—rich with life—and still we did not know why.