Isn’t it strange that every hole in the ground is now described as a “sink hole”!
Notwithstanding that if the paved area is part of your lot and/or if the stormwater pipe serves only your lot then the repairs could actually be your responsibility, the Owners Corporation’s building insurance covers only defined events with the emphasis being on that last word (i.e. “event”), which implies a coverage for point-in-time incidents and not for subsidence arising from the gradual deterioration of an asset such as the stormwater pipe in your 24 year old Plan.
So in my opinion your Strata Manager’s advice is correct, although that’s not to say that the Owners Corporation could not instruct them to submit a claim to its Insurer for determination.