[Marco Tahtaras]

Originally Posted by d.j. moordigian

So,...when it went from an "A" to an "18" , is it a correct part?
I've never seen the remains......

No, it was for the V8 distributor only. It had the depth for a plug to be held by friction. As a side note, I'm confident it was never intended as an insulator, but as a seal against moisture.

There was a Service Bulletin note (can't locate now) that essentially said replace the wax-like plug (meaning reinstall?). Ford never offered anything through service to replace it suggesting it wasn't exactly feasible. If you look at my pic below of an NOS distributor (which a previous owner dug out the "plug") you'll see the residue from the plug all the way to the base of the screw slot.

All these facts together led me long ago to conclude that what was installed as the plug was done so in a soft state to fill the shape of that shallow area and adhere. This could have been done with something that would cure similar to caulking does or something installed while softened by heat. That is why I suggest it required a special tool to form that seal or plug. Additionally, I also believe it was always done by the supplier and never by Ford.