As Leroy stated, the elastomer gives out over time one the OE units, and even the performance counterparts require 'rebuilding' to replace the O Rings in the dampers.
Which is why Fluid Dampers are so popular.
BTW, if this is the case, and the damper has slipped, the wobble will grow over the length of the pulley. Basically exaggerating the runout.
The best way to confirm the issue is to put a timing light on it to see if your timing is off from your normal setting.
Also too, look all the way around the damper to see if rubber is pushing out between the hub and outer ring.