Unfortunately for this poor 4-track deck, someone had vented their frustration at sometime and there was what I can only describe as a fist shaped mark in the front of the unit. That coupled with the lack of knobs, broken play pause, and seek buttons left the deck in rather a sorry state.
After my comrade in arms had attended the internal damage, replacing and repairing the fragile deck mechanism, he was left with a dilemma, in that operating the buttons on the unit with a screwdriver probably wouldn't be acceptable to most users of the device.
Debating the repair of the existing buttons was not on the cards (they were all missing), the only option was a bespoke production run. I will add at this point the deck in question had a sibling, which by per chance was in much better condition and had all it's knobs and buttons.
Using an existing button, we set about the painstaking task of measuring the exact dimensions and re-creating the design in Sketch-up (a lot of CAD elitists give this Google product a hard time, but as a beginner needing a quick and accurate 3d dev tool, I have found nothing better).
After an hour of designing and refining, we had something that resembled the original item, albeit a little thicker where we could spare the space, and a little simpler where we could get around the need for complexity. An export was made to .stl and Cura was fired up for a 3D Print run.
3D printing showed we were not a million miles from accurate, but also showed us exactly how precise these needed to be. A single miller meter of inaccuracy at the pivot bar, magnified to 5mm at the button height and working face of the lever.
More refinements were made and we got the final design licked in another hour or so. During the messing about with the button, we decided a break was needed, so I whipped up a knob (oh-err) to replace the missing items on the unit.
Anyway 3D batch printing the parts rolled in at about 4 hours, the parts were cleaned and filed, still didn't fit (well they went in, but some controls were held under pressure, preventing others from operating).... So everyone's favorite rotating mini-multi-tool was called into action to take down the offending lumps and bumps and hey-presto.... A working set of buttons.
It felt good to have this nostalgic little device running again, not least as they seem to be in demand at the moment.
This should have been a fun project! I am having the same problem, I have a great working X26, only the forwarding button has broken. Is there any chance you could share the STL file for this button? I was also thinking to have it 3D printed.