Mostly all the Fans in my PDP-11/24 and PDP-11/44 systems placed in the L-Box (BA11-A) are damaged, which is a big issue as they have an unusual voltage and frequency.
There are 3 Fans in an BA11-A which are responsible to cool the Card Cage and the Power Supply.
I was able to buy 3 NOS Fans, but they were so expensive, that I was searching for a way, to repair the old Blowers.
In the last Haul were a version of the Fan, which can simply be opened to replace the ball bearings.
This is great, as there is not much more than the ball bearing, which can be go bad.
After some investigation and measurement I have found a reseller, where I can get some types of the bearings in two different qualities.
I have chosen the SS R166 ZZ version, and have started to change the bearings. Each bearing costs about 1,50€.
Here is the process in pictures: