Ed,

  I certainly qualify as an "enthusiast", but I'll have to admit
that I've not done any heavy investigation into the chemistry of bore
cleaning.  I've used #9 for nearly all my shooting years (~50), and
your observation may be valid. I don't think it "dissolves" lead
itself; rather, it weakens the bond between the lead and the metal
it is stuck to.  It still takes a bit of scrubbing with a wire
brush to get the lead smears to break loose (less if you let the
cleaner sit in the bore for a bit.)  I'd think that would be less
of a problem with spark plugs, since you don't have the same level
of mechanical infusion of the lead into the surface. (At the
beginning of the bore, pressures at the base of the bullet from
propellant combustion are in the range of 30,000 psi (pistol) to
50,000 psi (rifle).

Looking forward to your report.

Dale R.
COZY MkIV #1254