[lexuspilot]

It clearly states in the manual "under no circumstances let the back of the perforated leather get wet" Since you didn't start cleaning right away, I imagine this is what happened. So the leather hardened. Maybe instead of acid it was water and the booze; alky-haul is known to dry things out.

If there is nothing visible, dried puke etc, then I would go with the suggestion above and condition the helll out of it and work it. If it messes it up , you are no worse off.

I am not an expert but had to fix a simlar problem once.