My Commodore C128D computer (plastic case) from way back had an annoying fan that sounded like a VAX 11/780 starting up. I just found out how easy it is to replace this fan with one that is silent and will hopefully last for another 40 years.
The fan can be simply reached by unscrewing the internal power supply and lifting it out.
The next picture is from the original fan that was installed. The 12V DC/0.2 ampere fan has the dimensions 60 x 60 x 25 mm and comes with a 3-pin connector. It is mounted directly underneath the power supply with four fitting metal screws.
I found out that the Fractal Silent Series R3 60 mm is a perfect drop-in replacement for the original. It has the same dimensions, runs on 12V DC, has the same 3-pin connector, and has a more modern rifle bearing:
I mounted the fan with four little foam spacers between the fan housing and the power supply to damp any vibrations from the fan. The original metal screws were just long enough for this.
After installing the new fan it makes fun again to tinker with my old retro computer from time to time.