File sharing settings

I recently updated two of my Macs to El Capitan, and by simply checking the File Sharing box under System Preferences/Sharing, I can share files back and forth between either Mac - wonderful.

However, I have an older Mac running Leopard 10.5.8 that won't get upgraded and I can't seem to access its files from the newer Macs. When I turn on File Sharing in the Leopard unit I can see it in the Finder under Shared on the newer Macs, however I can't connect to it from either unit - nothing happens when I click on "Connect As" in the Finder. Now from the older unit I can access files from either of the newer units, but not the other way around.

The nice thing about El Capitan is that there is nothing to set under the System Preferences Sharing menu. However on the older Leopard unit, I have "Options" where I can select sharing by AFP, FTP and SMB. I've tried turning them all On and in various combinations but I just can't connect to the Leopard unit from the El Capitan units.

Any suggestions?