Beogram 4000: Replacement of Broken Off MMC Cartridge Mount with 3D Printed Replacement Assembly

I recently received the tonearm of a Beogram 4000 from Belgium. It had a broken off MMC cartridge mounting tab. Sadly, this happens to many Beogram 4000s since they used a plastic that seems to go brittle over the years. Luckily this Beogram 4000 has the old-style MMC adapter insert that connects via spring terminals to a narrow circuit board that sticks in to the arm from the back. This allows easy removal of the arm by just removing one screw and pulling it out. This shows the arm as received:

The plastic tab that inserts into the MMC cartridges is missing and only the flex PCB with the contact traces remained:

It turned out that the plastic insert was glued into this particular arm. This meant I had to simmer this arm for an hour in boiling water in order to soften the glue. After I removed the arm from the hot water I was able to push the assembly out from the back with a rod that fits snugly into the arm. This shows the extracted part:

Luckily, the lower part of the MMC mount with the grounding tab was still intact and could be reused:

The next step was to assemble the replacement part. The first step was to glue the new nickel and gold plated contact traces into the 3D printed plastic part replacement, and transfer the wires over:

Then I assembled the insert. I used a damaged cartridge for positioning the lower part with the grounding tab that it was flush with the installed cartridge. Then I glued the back part with the spring contact tabs onto the 3D printed part:

This shows the back contact tabs after assembly:

The next step was to insert this assembly into the arm in a way that the mounting screw would go straight into the back part while ensuring that the cartridge was snug with the aluminum tube. This was the result:

This is how the MMC mount looks like without cartridge:

Pretty close to the original! This arm is ready for duty again!