Randy,
When I transferred my groups from Yahoo all but one went well. One of
my groups did not transfer over the "files" and "attachment" sections.
Attachments weren't copied over for any groups.
With Files (and Photos) it depended on whether the agent could access them at the time of the transfer. The advice had been to wait until access to the section seems to be working, then delete the record of the transfer from the Existing Transfers list then set up a new one, this time deselecting everything except the missing section (Files or Photos).
However with the transfer mechanism shut down at the moment I'm not sure what to suggest that's any better than manually uploading them folder by folder.
The download side you may be able to improve upon by using PG Offline, a product of Personal Groupware:
Shal
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