I've had a look through the various versions of Slipping / Slipping Again.
I would agree that the levels could be moved earlier, and I also think they should be further apart, so perhaps Slipping in Cunning and Slipping Again in Daunting?
I don't think anything needs fixing -- everyone's replays for Slipping Again are all variants of the same solution. This was not meant to be an "anything goes" level, but any solution that finds the core ideas is okay. The level could be tightened by removing two (or even three) builders and a basher, if desired (or one or two builders and both bashers) -- though keeping the extra skills makes execution easier.
I really don't want the levels to be swapped out -- they are good puzzles, the idea for Slipping Again is not easy to find (and thus rewarding when you do find it) -- Ramon's comment in chat when he solved this puzzle was "Very nice
". I just don't think they necessarily belong in Vicious, and perhaps they would have been more favourably received if they'd been placed earlier to start with
Mobius' remake of tseug's Slipping has a backroute (essentially the same one Nepster found), so it can't be used unless fixed, and I haven't found the intended solution yet. In spite of the identical title, this is a completely different level, so it shouldn't be thought of as a possible alternative for replacing nortaneous' Slipping.