My real estate agent didn’t make us sign form 300 -BRA. Isn’t that mandatory for the real estate agent to sign ?

We’ve sold our home - closing is at the end of may. Yesterday we noticed our hot water tank (7 years old) has a slow leak by the heating element (which we know is a replaceable part, as long as the inner tank isn’t eroded). I’m with the understanding that if it can’t be repaired we would be obligated to install a new tank, my husband is arguing we’d only pay for the appreciation of the tank similar to an appliance (if your 10 year old oven goes, you’d only be obligated to replace it with a 10 year old oven). To me a hot water heater is not an appliance but a plumbing fixture.

Just want to make sure we’ve covered all our bases, before paying for the tank replacement.