Thanks very much for your reply, kasbah! Sure, here's what I get:
/etc/hosts file reads as follows:
When I combine port 10051 (on the right) with 127.0.0.1 in the host field and tell it to connect, it immediately connects and changes the host to "Firstname-Lastnames-MacBook.local" (putting "firstname-lastnames-macbook" into the host field achieves the same effect, as does leaving the host field entirely blank) -- and "Firstname-Lastnames-MacBook" is what my computer is named in my file-sharing preferences ("Computers in your local network can access your computer at 'Firstname-Lastnames-MacBook.local' -- if the wording's not entirely correct here, it's because I'm translating it back from German...).
Aside from all this, strangely enough: when I press the "defaults" button, what I get is port "9951" -- whereas AU Lab shows me "10051" as the OSC server port (which I assume is the relevant one?). Trying to connect using port "9951" produces no reaction. Apparently this is a different default than the default startup settings ... although SL has apparently stopped being able to find those upon startup, since if it were able to do so, I assume it would be able to connect on its own, like it had been before...
If it's any help, today my load/save dialogues give me a blank field and above it is written: "Choose file to open on remote host "firstname-lastnames-macbook.local" (I think that in the recent past its also told me both "...on remote host" and "...on remote host localhost" -- for what reason(s) I have no idea...)
Apart from all this, another little bit of weird behavior: whenever I try to save midi bindings (as in: simply press the "Save" button), SL has been reliably crashing over the past few days. If I try to load midi bindings, SL will give me the usual single blank field and either "load midi bindings" (today) or something like "load pan_1" (yesterday) -- even though I have no binding set up for any panning functions to begin with ... although I did try that once a long time ago -- it's like SL is randomly tapping into all kinds of hidden, obsolete preference settings stored only God-knows-where... luckily, it is still finding the correct session and midi-bindings. For the moment, at least.
It now occurs to me that this latest episode began after I'd tried to create an AU Lab setup with a mono input, wanting to then create an SL session using just a mono loop. AU Lab refused to do so, crashing and of course taking SL along with it (I think it was upon selecting SL as a bus that it would crash). It may be that this somehow corrupted the preferences that SL had been using, and that SL is now resorting to a hodgepodge mix of older preferences -- once again, stored only God-knows-where -- that don't work together and render it lost within the machine. Just a wild theory from someone who's way too unknowledgeable about these things.
I'm assuming that this is actually a minor, silly little problem that's easily solved, but to someone with my level of knowledge (= professional musician, zero training in / knowledge of programming) it defies all human logic ... I very recently got confident enough to try using SL in a professional setting, but the present impossibility of calling up a pre-stored loop (which I need once during the performance) or, for that matter, knowing whether it's going to work at all from one day to the next means that I will have to ditch it unless I can find out how to reliably fix this issue (and I'm still really hoping that I can) ... it would be a shame, because apart from this one problem, I love using SL.
Any ideas would be much appreciated!
(and sorry for the lengthy post, but I assume that in cases like this, more detail is better than less)