Re-colouring remains sticky and no stickiness!

Leather remains sticky and pigment does not penetrate!

Only on a base the pigment does not seem to penetrate and remains sticky.

preparation: Solvent cleaner, light sanding, re-cleaning, recolouring with black pigment.

On all the rest of the seats, but on a seat that is impossible to hang.

Note: old leather (25 years old) has no cuts or cracks. On the other hand very stiff, turned stiff by sun exposure I think.

What can I do to get the pigment to stick?