The base molding (two inches high) at an inside corner has about a 1/8"
gap at the inner edge (as though both miter angles are a few degrees
less than 45 degrees). The mitered ends (along with the rest of the
molding) were primed and painted before being nailed in place. What
should I use to fill the gap? The choices are wood filler, caulk, and
spackling compound. The filler will be painted.

Thanks,

Ray