If its cracking its too late.
Other than another saddle of the same type, you could possibly recover it.
Some saddles with vinyl covers were just thermo formed then secured over a base and various foam pcs.
Some have a layer of foam bonded to the vinyl cover then formed and wraped over the saddle.
Look underneath and examine how your saddle is constructed, if with staples and some glue there is hope.
A dart will most likely need to be sewn at the front to make vinyl or leather work.
Done both, but some were not worth the time investment, search ebay first.
A cobbler and or an upholstery shop might have material rems and glue you need, and be able to sew the dart.