In my experience, when you open up the Sharing option in LW's Preferences, it will open to the same directory in which the previous shared folder was added. eg: If I added folder A as a shared folder within folder Z, then the sharing addition would show folder Z as the 1st option to add another folder from.

But if it's gone, it's a mystery. Have you tried restarting the comp in Safe mode & doing repairs such as permissions. Then restarting (The system may need a breath of fresh air.) There are utilities that can turn all invisible files within osx to become visible. Question is how/why LW stopped sharing in the 1st place.

If your alias stopped working then that sounds like a system problem. Bit of system refreshing could help.