Help with my Explorer II

[lap513]

My Explorer II, is about 4 years old. I bought it new from an AD here in Atlanta. It has worked fine up until now.
The watch will keep good time if it is on my winder or fully wound and sitting, but when I put it on my wrist after a couple of hours is stops. Never had this problem, I know it probably needs servicing, but it shouldn't be stopping. The first time this happened I wound the watch and put it back on my wrist and it stopped again after a couple of hours. Then I put the watch on the winder, and checked it for a couple of days. Kept fine time while on the winder, put it on the wrist and it stopped again. Confused.