How can I get a China visa if my E-2 visa has only 4 months left when I wish to travel?

I'm a US passport holder, living in Korea on an E-2 visa. I want to visit China. I've been told I need to have a minimum of 6 months remaining on my E-2 visa in order to visit China and be allowed to return to South Korea. Is that true? I've got 2 years remaining on my US passport. I will only have about 4 months left on my E-2 visa at the time I wish to travel.