Confusing Radiator Leak

[cedarheaven]

1994 F-250 just turned 140,000 miles. I take better care of this truck than the little woman. She began with a little weeping from the passenger side fender panel. I let it go for a week to see what more would happen...waiting to see if the heater core was going bad. This morning, I found a little green puddle on the backside of the radiator around the top seal and "cap." I have used Bars Stop Leak on other occasions in the past and have had very good luck. Although hesitant about putting the Stop Leak in this vehicle I need to put a stop to this leak and am asking this question????
WHAT is the best product (Stop Leak) for my application? Stock 1994 Ford F-250 I'm sure it has the stock Ford radiator. For starter's, I am not too thrilled about the copper pellett product...I appreciate your comment's!

Thanks