I've got some horrendous surface cracking in the butt-cheek leather on my 98 LeSabre:
I'm using two products recommended by this place:
1) LSF (leather soft fill); a sort of a "cream" heat-set polyurethane to fill the cracks
2) ColorBond; an OEM color-matched rattle-can leather and plastic coating (similar to the SEM system)
Prep includes fine-sanding down rough edges, then clean with a 5% Woolite / 10% rubbing alcohol / 85% water mix (like SEM soap), then wipe with acetone (like SEM prep)
Then fill the cracks with LSF, "squeeging" to even with the surface. Set with heat gun.
(Note: LSF is not meant to repair tears or holes...just fill those multiple feather cracks in the surface coating)
Clean it up again, then spray with ColorBond.
I did my steering wheel with the Colorbond a week ago, as the brown leather underneath was showing through...it'* held up very well so far, and colormatch was perfect. I'll let you know how the LSF / ColorBond combo works out on the seat cracks.