The 1951 Pfaff 131 is in very good condition. It worked fine except for the fact the zig zag dial was frozen. Probably caused by old oil solidified on the dial shaft.
Even soaking for several weeks in penetrating oil and brake cleaner didn't free the shaft.
Finally the shaft was freed by using a heatgun. It didn't need much heat to make the shaft move very easily. Now that the shaft could move without the dial, the dial setting was completely out of adjustment, so it took some time to find the correct setting, but finally the machine was sewing and zigzagging like a new one.