costs before inspection

[Kosh Vokter]

Evaluating an off-market property in AL. We took pictures / videos of the property and there is some mold on the drywall in the garage from a previous water heater leak. They have since replaced the water heater, but there is drywall pulled out and some mold on the drywall from the water leak. We know that this won't appraise as is but don't know the source & extent of water leak damage. We want to remove/demo some sheet rock near the water heater to look for the extent of damage and mold issue BEFORE we get an inspector out for inspection. Sellers don't have money (~$500) for removing the sheet rock, and they are okay for us to hire and pay for our own licensed contractor for that work. 

Current Strategy: We wanted to add an addendum to the contract so that we have this written down (i.e. buyers don't assume liability if there is a problem/ other damage while contractor removes sheet rock) with seller. Get the contractor come out to remove sheet rock and then hire and inspector to do a thorough inspection. 

Is this (Addendum in the contract) an acceptable risk or any other strategies that you recommend? The other option is to walk away and not go the contractor route, if this strategy is risky.