During a complex and long print, one of the stepper motors broke down. Apart from the fact that it was really mean, so shortly before the end, you have to get the motor going again somehow.
A complete replacement of the engine is expensive, so open the engine and see what exactly is broken. The ball bearings are leaking a sticky mixture of metal shavings and lubricant. If you remove the cover from the ball bearing, you can see that everything inside is full of rust, which is blocking the bearing.
If you take a closer look at the ball bearings, you can see why. The type designation 625 Z states that the bearings are to be sealed by metal cover disks. As the motors get warm and the metal expands, lubricant can leak out, which is supposed to prevent corrosion. corrosion.
You can fix the problem relatively easily by buying new ball bearings with plastic cover that seals better. (625 2Z)