If PDF-TeX Sync support is set to "TextWrangler" and I cmd-shift-click into a document, Skim tries to launch (in this order)
/Applications/TextWrangler.app/Contents/SharedSupport/edit
/Applications/TextWrangler.app/Contents/SharedSupport/bin/edit
/Applications/TextWrangler.app/Contents/Resources/edit
/Applications/TextWrangler.app/Contents/Resources/bin/edit
/Applications/TextWrangler.app/Contents/MacOS/edit
/Applications/TextWrangler.app/Contents/MacOS/bin/edit
/usr/bin/edit
/usr/bin/bin/edit
/usr/local/bin/edit
With the current version of TextWrangler (4.5.7), "edit" is located in
/Applications/TextWrangler.app/Contents/Helpers/
so you might add that location to the list. At present, "sync" only works if the "TextWrangler command line tools" are installed, because then "edit" is copied to /usr/local/bin.
That's stupid, as Helpers is not a documented location, as opposed to the other locations. I really consider this a bug of TextWrangler.