I'm a 51 year old Greek citizen with a US green card, I've lived in the United States for 38 years. I've been told by a relative who recently travelled to Greece that, if I ever travel to Greece upon arrival I will be obligated to pay a fine of $3,000US dollars and serve 40 days in the military. Does anyone know if this is fact. I left Greece when I was 14 years old and have never returned, due to this. can some one help?

That is absolutely untrue. Any military obligation to the Greek state ends at age 45 per law 3421/2005. If you can read Greek, you can find the relevant passage at http://www.stratologia.gr/N.3421)05.pdf