OT: I wonder if some color sealants crack more than others or if it depends on the batch? Or maybe the climate each bag is in? I've had two St. Louis' and neither cracked like this. My white had some tiny hairline cracks but my green has absolutely nothing and I've carried it almost daily with a laptop etc. for two years.
Back on topic: I think the price is steep for replacement straps, but if you plan to continue to use this bag on a regular basis, I would consider it.
I live in Continental Europe and have experienced cracks on my yellow PM St. Louis after only a couple of weeks of very moderate use (I definitely am no pack rat and hardly ever have more than a wallet, agenda and small cosmetic case with me. Okay, plus mobile but thats it).
I find this extremely disturbing and not okay for a $$ bag... The cs for sure is ne help...