Visit the ClockSavant Instagram page to see a combined photo/video showing a few snapshots during the servicing of a vintage high beat King Seiko with caliber 4520a. The microscope video shows inspection of the hairspring revealing light rust. I see this on about 1 on 10 watches and is often due to improper solutions and drying during past servicing. The wheel attached to the bridge shows the use of excess oil. Click here to see the ClockSavant Instagram post.