Universal Polerouter Cal. 138 SS Bumper
The Serial number 1'711'970
puts the age of this Polerouter at 1955 to 1956. Fellow PMWFer Chris was so friendly and post the Universal serial number year of production table.
Opening the case back was a bit tricky
even with my Bergeon 5700Z opener. The case back was stuck! Really stuck. Instead of adding more opening marks to the case back - please note, some previous opening attempts left some deep scratches and even deformations - I decided to use the "oil soaking method". Simply apply a generous film of fine oil around the edges of the case back and let the oil do the work for 24 to 48 hours. And after two days of soaking, the case back would indeed move at the second attempt.
After the case back was removed, I was then also able to remove some of the marks and even deformation from previous opening attempts. So the case back looks actually much better than in the picture now.