Heh, heh, I was speaking figuratively in the sense that something had altered and often at the moment all that needs to be done is to adjust the alignment of some element of the system, rather than actually changing components. The headache of doing a lot of experimenting is that the everything starts to become rather messy, and fragile in the sense that the optimium positioning and stabilising of things can be easily disturbed. Mike, for example, talks of the need to reset his isolation supports because they can make such a difference if they are not right, and that's usually the sort of issue for me at the moment.
But to talk of solder: I'm not fussed, I just use the standard, everyday, lead/tin stuff. I believe the actual quality of the soldering job, how well it's done is more important, and even though I have not investigated this at all, a very meticulous ensuring that the thickness of solder between the copper, hard metal elements is as thin as possible will benefit the SQ, IMO. I have gotten away with being fairly sloppy and I'm sure I could improve things by taking more care ...
In the overall scheme of things, my experience is that other factors are more important than the soldering. Such as the quality of non-soldered connections: I know you and others have moved away from silver contact greases but my experience is that these are very positive tweaks. Again, the trick is to be very careful and precise in applying these, everything as clean as possible before applying, use only just enough to do the job, make the connection as tight as you possibly can and then do not disturb this connection!
Frank