First leak I’ve seen
And I’ve seen some that are pretty bashed about
You might check for your bank or cc statement and offer in lieu of receipt, though if you’re a regular customer at the shop they may be able to sort things even if you paid cash
If your tank has a date stamp showing it’s manufacture within the warranty period, Fluval should replace without question
Sometimes (ofttimes?) manufacturer’s are more responsive to shop backed inquiries, so I’d begin there