Withholding $ on property transfer for repairs

Hi all
Has anyone had any experience as a seller/buyer or in the legal field as to what is the best course of action to take where a problem has arisen that requires building works. ( refer original post “Building Inspections – worth it”)
As the buyer my companion needs to be covered to ensure the problem is fixed. The scope of works have been defined in a building condition report commissioned by buyer – major leak in at least one possibly two bathrooms in elevated home. Possibly effecting downstair rooms. Sub floor works likely. Home is only 10 years age.

Thus far we have been given several pieces of advice:
1. Owners fix problem and maintain purchase price.
( However as buyer you have no control over quality of workmanship and has it been fixed ??)
2. Settlement goes ahead at agreed purchase price less negotiated rate to have works done.(Owner obviously wants cheapest quote – no guarantee of can of worms extra costs might be involved that purchaser would have to bare)
3. Settlement goes ahead but withold a provisonal sum that allows for the works to be undertaken to fix problem. Cost of fixing problem deducted from this.
( Buyer has control over works – can of worms explored when builder gets into areas involved. But this would be like a blank cheque if i was the owner !!)

Any ideas gratefully appreciated.

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Regards

“Do not follow where the path may lead. Go instead where there is no path and leave a trail” Ralph Waldo Emerson