I have a 249E from the pre war era, still runs good. The older engines need more service to keep on running and I would suggest cleaning the armature brushes and contact area on the armature, I use a pencil eraser to take the crud off the armature and brushes. If the brushes have a small pit mark or are uneven a light sandpaper will smooth off the surface of the brushes. Lube the gears & axles as well.
Lee Fritz