That seems very unusual. Did you lubricate a pivot or two after cleaning and work it in? The lubricant can also help any grime flow out. Since it's affecting all tools though it must be something with the liners or the spring has really gone... how it the tension on the spring when the tools are open?
Is it possible for folks in the U.S. to send a Vic to Switzerland for repair? I have now sent two SAKs to the US repair center, and both have come back the same as they left (weak/no snap, other issues), it looks like the only thing that was done was to sharpen the main blades.It would stink if you also send your knife off only to have it come back the same as you sent it in.
It's hard to say without having it in my hands but it sounds like the middle pin (where the back tools are mounted) is either bent or broken. :- It would certainly explain why moving the back tools adds snap to the main tools. I've never had this happen to any SAK I own, nor can I remember hearing about it either, but it's always possible I suppose.