Hi, I got an issue with my vintage 401. Its a G version made in Germany but the internals are pretty much the same as with the 401A. After sewing for about 10 minutes the machine starts to slow down, to the point that it completely stops and becomes very hard to turn even by hand. The machine after a while starts going again, maybe after it cools off but slows down again.

Anyone ever experienced something like this? Any pointers on where to look or what to do?

I posted a video on youtube with the problem https://youtu.be/VIpr4qFMpMU

Edit: the machine is fixed. Took the motor apart and cleaned everything well, put back together and its running much faster and smoother. The collar where the brushes sit was gunked up so took a fine sandpaper and cleaned the collar. Thank you all for the suggestions