My inclination would be to put the correct spelling in the Place field of the Fact; but let the incorrect spelling in the record stay in the source (probably in the Source Title or the Source Detail).
This is not much different in concept than adding the county to a place name in the Fact field - but leaving the place name in the source as you found it - which often won't show the county.
Whether you can change all 40 sources at a time depends on where the place was entered and whether the citations were separate (by using Paste Duplicate) or the same citation (by using Paste Link).
If the name in the source is coming from the source title - changing that source name will show in all citations from that source - whether duplicates or paste-link clones.
If place is in the place citation detail or text and the citation was attached to various facts by Paste-duplicate, the change in place name would need to be made in each citation.
If place is in the place citation detail or text and the citation was attached to various facts by Paste-Link, then changing the place in one of them will change all of those citations.