Is log file name represents current date and time? If yes, then for that pattern active log file can be identified as following:
<file>AMS3AutoDealerLog%H%a%d%b%Y.AMS3</file>
Logwatch will automatically switch to new file each hour.
But if log file name contains past hour, not current, then you will need to create external script which will provide logwatch with file name to parse. To use script for generating log file name, use following syntax:
<file>AMS3AutoDealerLog`my_script_name`.AMS3</file>
Best regards,
Victor