valvoline oil pam clock

i have a 15" round lighted clock made by the pam clock company. on the face it says "valvoline" right across the center. above that up near the top it says "ask for". and near the bottom it says "motor oil". i bought this clock because i like it and im putting it in my new garage, it keeps time and works great, even lights up with 2 little 15 watt bulbs. what i would really like to know is when this clock was made, im guessing the 50s or 60s but i dont know how to date it.