Before 1980, everything was electric at best. After that time, electronics began to advance. And electronics, that's cunning stuff. It works or it is broken. And when it breaks, you are sitting with a non-functioning car and you are angrily looking at a solid black box with a set of wires and a few multi-connectors.
If you're lucky then, the malfunction was in the transition resistances of those multi's. But otherwise? My universal meter and I usually do not know how to handle such a box. We have not learned enough for that. Moreover, I am mechanics, not electronics. I understand working on a conventional electrical installation and its components. But electronics? No.
When you then look for replacement news, you have the chance of a cold fair coming home. When electronics ended up in cars around the mid-1980s, the parts were mass-produced for generally impressive numbers of cars.
About ten years later, the recycling of parts was really well underway. Containers of new old stock of ECUs and other electronic wonder parts were transformed into heat and raw materials. And were thus effectively withdrawn from the parts provision.
Therefore the tip: Youngtimer lovers: now score what you can score. Finding board electronics, window motors and such is not always easy anymore, but when you still find things, they are often surprisingly cheap.
Your partner may rightly object to a set of oil-leaking engine blocks in the attic. But a few boxes with electronic things can easily be stored in a cupboard behind the roof boarding.
And if you do not need them: in twenty years they will be worth gold.
Finally: sometimes you can find untraceable components by searching for serial numbers in the manufacturers' catalogs. Electronic car parts actually come from a limited number of global manufacturers. And the customers of those manufacturers regularly use the same things for different models in their own production line.
Once there were De Hollanders Guides for Interchangeble Parts. It is time for something like that to come for electronic components. Because how else would you get the idea that BMW used the same electric motor to operate a sliding roof that was used to adjust the windshield of a BMW motorcycle?