Just adding on to this in case anyone stumbles across this on a Google search as I have, the issue persists even on the updated 2022 Utopia, much to my chagrin. The plastic mounting ring on the back of the earpad is coated with a soft rubber/plastic-like material that has a tendency to liquefy, not unlike the rubbery coating you'd find on cheap earbuds or electrical wiring of yesteryear after prolonged periods of storage. I first noticed it as a weird oily substance or goop like the others here have described, which kept leaking out no matter how much I'd wipe down the earcups, so I took out the pads and wiped them down too but noticed they'd eventually start leaking again as well.
As such, I've gone for the nuclear option and used isopropyl alcohol and a sharp implement to completely scrape off the soft outer layer (leaving the harder plastic with the connectors needed to reattach the pads to the earcup frame) and so far there hasn't been any recurrence of leakage, though i would advise care when using water to wipe down the cups after you've removed the soft layer since the stock Utopia pads are fenestrated leather and I'm a bit concerned that the moisture has overly-softened the memory foam underneath, which may change both the fit and possibly sound characteristics of the pads (they feel a little less firm than from before the cleaning).
I'm hesitant to get replacement stock pads from Focal given the outrageous price ($250) coupled with the known defect of the melting mounting ring layer, but I'm not too sure how well 3rd party stuff like ZMF or the Dekoni pads maintain the Utopia's sound signature.
Honestly still not entirely sure what triggers the whole melting thing to begin with- I started noticing the breakdown after about 2 years of regular use as a daily driver, and the environmental heat and humidity may have played a role.