I entirely agree with Graham that the case does not carry genuine Chester hallmarks.
A number of similar American made gold cases have been seen and it is not uncommon to find the winding hole cutting through the hallmark, as in this example. Another point to note is that the crown on the Leopard's head.
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This particular design of punch was introduced in 1794 and in continual use until 1822, when the new punch was introduced, depicted a head without a crown. As you can see your example has a well defined crown. However, by ~1810 the definition of the crown had become far less distinct. Here is an example taken from a genuine (silver) case of 1813/14 with the date letter 'R'
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As Graham has indicated your Johnson movement is probably from the 1820's, I suspect the middle of the 1820s, by which time the Leopards head should not have a crown, and even if it was =<1822, the crown would have been very indistinct. It is common to find these discrepancies when faux mark are examined.
Many of these movements when exported, were capped. Your movement has the posts to support a cap - compared with a capped movement below ...
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Is a cap still present? If so are you able to post a photograph of the underside - it may carry a maker's mark.
John