I’ve had one or two of those old Japanese machines that had tension assemblies like you described. The barrel of the tension assembly is some kind of “pot-metal” that seems to swell into the casting hole of the head, like a mushroom. The metal quality is so poor, that the part that I could get hold of to remove it crumbled easily. I’m not sure what conditions the machine has to go through for that tension barrel to mushroom like that. Heat? Humidity?
I’ve had to chisel them out and install a new tension assembly.
CD in Oklahoma