This time In added a number of large and small M4 washers and placed my fan deeper.
Also: Powering the fan and Raspberry Pi from the same 12V supply seems to cause random crashes of the Makibox firmware. Particularly when it's supposed to start heating the hotend. I have gone back to powering the Raspberry Pi via a second power supply and am observing the situation to confirm this as the cause.
Result: It still crashes. Something else must be at fault. Searching...
The washers are perfectly cool.
The PID control has a hard time reaching target-temperature and usually stays 5°C below what the hot-end should be at. I will need to change the PID settings or block air flow from cooling the hot zone instead of just the washers and shaft.
The bed needed to be leveled again because the length of the hot-end changed a bit.
The TEST PRINT FAILED AGAIN with the same filament stalls as all the others.
At the time of failing the washers where perfectly cool.
I changed the target temperature to 218°C.
This is a temperature that worked well before and has less mechanical resistance because of lower viscosity.
I changed the target temperature to 190°C.