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

 

The under hood temps and being in the southeast is what did those urethane bushings in. Yes, it’s also possible that they were not meant to handle engine bay heat. Rubber is really the best for the engine bay to handle.