Finally the breakthrough!
I can now confirm that there is already a tiny hole at the very corner of Santa Catarina Plane, which is indeed the exit of Highway 1.
That means loch number 5 - the first naturally created loch - is now reality. (The other 4 have been bonked by myself.)
Many thanks to each member of Expedition I for all the hard work and excellent team play.
The new hole shall be called Loch Eck.
Note how amazingly fitting this name is: According to official naming policy, it had to be a loch from Scotland starting with the 5th letter of the alphabet (which is "E"). Now "Eck" in German translates to "corner" and - here we go!
By the way, if you are interested in the "real" Loch Eck, go here.