Bubbly fluid is not good:). I'm guessing rotting is happening under the older leaves. If you bought it yesterday I would try to get your money back or a replacement:).

Is there really fluid there, or is it the new body peeking out from that crack, while the old leaves are being resorbed?

I can't really see any liquid from the picture. Their tops (windows) are usually transparent though so it might just look like it's some kind of out of place liquid. Is this your first time owing a lithops or have you had some before?