lefty – so in the circumstances where the glass splashback as originally fitted to a common wall did, as you’ve now clarified (thanks) spontaneously fracture, the repair and/or replacement of that is the responsibility of the Owners Corporation (O/C), and irrespective of whether it elects to meet the consequent costs itself or to claim those against its building insurance, the entirety of those costs including the excess in the latter case is the O/C’s responsibility.
The only “out” for an O/C in circumstances such as yours is a Special By-Law where, under the provisions of Sect 62 (3) of the NSW Strata Schemes Management Act (1996), it could at its discretion specially resolve that “it is inappropriate to maintain, renew, replace or repair” a particular item of its common property – namely the splashbacks.
However your O/C has lodged an insurance claim, so I’ll assume that it hasn’t adopted this provision, and reiterate that under that scenario (or any other) you shouldn’t be one cent out-of-pocket.