I have several older (1960s) Japanese pens that use a thick rubber gasket between the coupler ring or cartridge nipple and the feed, unlike newer pens, these often have enough "stick" from their thickness and being compressed in the section for decades, that they don't just push out the back of the section when released. I had previously just ultrasonic cleaned these for hours on end, in order to get the feed diffusors clean of old ink and written ones that needed nib work off as unrepairable. Then I got to thinking about thin bodied silicone and the possibilities of using it as a release lubricant. Applying a drop from the back (gasket) side of the section releases, or greatly reduces the grip from that rubber gasket and in the two pens I've tried it on makes disassembly possible. It also washes off with soap, or an ultrasonic cleaning. I used Super Lube brand 100% silicone with a 100 cst. (centistoke) thickness, it's very cheap ($6/4oz.), readily available and like any 100% silicone product, it's chemically inert and shouldn't damage any materials, with the possible exception of silicone based polymers.
Of course YMMV.
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