First, you must know that it's probably the vinyl side of the seat that is cracking. I've just joined this 'club' after sending another comment to Nissan National.
I have a 2004 Murano, with only 61,000 miles, and both front seats have cracks on the outside side panels.
"Out of warranty" was the reply I got from my local dealer.
If no better response comes from the national representatives, I plan to embroider on a piece of vinyl or deer skin leather, died close to matching my Cabernet interior, the word NISSAN or MURANO to patch the damage.
I am disturbed that Nissan has let this matter go unresolved, and they will have to make the side of the seats of leather, if I purchase another vehicle from them.