The elusive but important "casing spring" >>

The "casing spring" is an extremely important but fragile component of the SEIKO Bell-Matic. Simply put, without it, the movement rattles in the case. Because of their thin, metal structure they are especially prone to corrosion and rust. Far too many Bell-Matics are sold without these springs, or with poor substitutes (such as movement gaskets) in their place.

Here is a link to an image of its technical info in the Archives:

And here it is in all its glory: