Mold claim denied as 'maintenance issue' but the source was a hidden supply line that burst behind drywall. How do I prove sudden vs gradual?

Bought our house in 2022. Last month I noticed a musty smell in the guest bathroom and a soft spot on the wall behind the toilet. Pulled back the baseboard and the drywall came off in my hand. Black mold across about 6 feet of studs. Plumber cut into the wall and found a slow leak coming from a corroded supply line connection that was hidden behind tile and drywall. He said the line was probably weeping for a few weeks before it finally let go.

Filed a claim. The adjuster came out, took photos, then sent a denial saying the loss is excluded because mold from "ongoing seepage or leakage over a period of weeks or more" is not covered, and the failed connection is "wear and tear / maintenance." We have a $10k mold endorsement on the policy and I assumed exactly this kind of thing is what it covers.

The supply line was hidden, no visible signs, no water bills jumped, no warning. How do I push back on the "gradual" framing when by definition I couldnt see it? Anyone successfully fought a denial like this? I am in Ohio if it matters.