If you search for the data first, then explicitly call the transform (like | extract secDeleteExtract) does it find the fields? I wonder if the base sourcetype in your props matches the data.
Next, since this is colon-separated, you might consider rules like this instead:
[secDeleteExtract]
DELIMS = ":"
FIELDS = stamp, action, ftpAccount, ftpClientIP, ftpRenamedFile, date
This tends to be a bit more performant than regex rules. You'll want to be sure to list every field (in this case, I've called the epoch time stamp 'stamp' in first position).
If you have access to the filesystem, can you try running 'btool props list field_sec_ext' ? This will apply Splunk's configuration layering rules to tell you what the running configuration would be for that sourcetype.
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