I can't believe owners corps and strata managers are still giving out this flawed advice. While painting the inside walls is, indeed your responsibility under normal circumstances – if damage has been cause by a failure to maintain common property, then the OC has to make good. It's a simple as someone accidentally bashing your car – they have to pay for the repairs. There is no argument with this – ask your EC if they want to organise the painting or should you just do it and bill them. Either way, they pay.