Newer style saddle with removeable girth staps, replacements can be bought. Approx £12 a pair.
Older style saddle take it to a saddler and get straps replaced with leather ones.
The biothane they use on the straps always cracks and exposes the polypropylene webbing inside which they frays with time. As previous poster has said convert to leather (much better) or renew yourself if the strap has a metal clip at the top, then they are the ones you can do yourself.
I had a wintec once-upon-a-time and one minute the girth straps were OK and the next minute they were in a dangerous state
Ditto their own brand stirrup leathers; so personally I'd check them PDQ.
This is why I HATE synthetic saddles; with a leather one you'll have plenty of warning if something is needing attention, with synthetic you don't. Awful things.
I convert loads to leather, the breaking strain on rawhide girth straps is around 5000-5500 lbs per square inch, lot tougher than biothane or polypropylane!