Black slime/goo people?

[Draug]

I have a friend who's trying to find the name of a movie that gave him nightmares.
He say that the cover (European cover?) shows three people like creatures covered in black slime. The movie is from between 1984 and 1988. The trailer shows that they are sorta coming up/out from the forest, and they are all covered in black slime/goo. One man is sleeping and you can see a black arm touch his face or something, infesting him. Half his face get covered by this goo who, trying to take him over. There were also some lights coming from somewhere when these ghoulish creatures emerged from the forest.

Any clues?

[akiratubo]

The cover and what happens to that guy sounds a lot like Seedpeople.  However, it's too late for your timeline and they weren't exactly "slime" monsters.

[sideorderofninjas]

There was the tar zombie in Return of the Living Dead. 

[Draug]

It isn't Seedpeople or Return of the Living Dead. He have a quite fascinating knowledge about horror movies and he's tried all kind of methods to find the name of the movie. Seems like a fun challenge to help him.
He said he found the cover on imdb.com a couple of years ago, but forgot to write down the name and then he closed the window.