I believe the Black Dog polyurethane bushings (sold by Welsh if I’m not mistaken) had a tendency to melt.

 

Might have to take a chance that they are 2 different manufacturers and different materials just the same black color

Might be the reason Welsh didn't reorder from the manufacture ( now they have no stock to sell from his inquiry to buy from Welsh )

 

I have a set of damper X308 mounts with MELTED BLACK material.
I threw them on a scrap pile and they continued to melt onto other parts in the pile.

My guess is someone put the one's you are talking about on a car and they failed so I replaced them.(what a mess)

 

Continued to melt may be the 2 part material never cured and not to do with heat , but you're in Texas

Catalyst ( cure ) is the most expensive part of the 2 part raw material mix