The oil should be changed if you have much leakdown.  However, a little won’t hurt; it will simply deplete the amount of B-12 Chemtool you have in the cylinder still.  As long as the liquid level stays above the entire piston, then you should remain in good shape for the cleaning. For best results, you can blow a little air into the cylinder during the soak to splash the B-12 around.  This can be accomplished using compressed air or even a “duster”—whatever is most convenient.  Just be cautious not splash the B-12 out of the combustion chamber as it can damage paint. Once you’ve completed the soak and removed as much of the liquid as reasonably possible, cover the cylinder head(s) and turn the engine over to force the remaining liquid out.    After putting the plugs back in and getting everything back where it goes, run the engine for few minutes to get the oil warm.  If you check its condition and it looks dirty, then you had leakdown and probably need to change the oil and filter soon (or immediately if it’s especially dirty).  If it has stayed clean, there’s no need to do another change already. The easiest way to tell is by putting a drop of oil on a couple different types of paper—computer/copy paper, newsprint, etc.—prior to doing the test.  Then do the same after the test and compare the colors.  If there’s little to no color change, then you can keep your same oil and filter change schedule.