Hi everyone. Have been a very happy owner of Flieger Classic for 3 years and time-wise, it has been great and only needed to make a minor time adjustment every month or so. The last few months though I've noticed it is running slow and if I don't adjust it once a week it will be well out of time. Just did a check and it amounts to losing 20 seconds a day - not good! This is my first mechanical watch so new to all this so just seeking advice on what could be done to address this? Movement is...

Flieger Classic losing 20 seconds a day