Always new in that if you have to buy one for what ever reason, buy a new one. Not expensive . You can't always do a visual and be sure it is ready to go. Why take the chance. Even if you get lucky and don't damage something, you still have to buy another one and do the work again.
An engine just passing someone on the road can hit 4,000 rpms. May not seem fast but think about it. A couple of pounds of iron/steel spinning at just a few thousand rpms is a lot of force. Even if it is only 6-8" in diameter.
A new 78-80 318 balancer is about $50. 78 1978 Dodge D100 Engine Harmonic Balancer - Engine Mechanical - ATP, DIY Solutions, Dayco, Dorman, Pioneer Cables, SKP, TRQ - PartsGeek
