Hi - my name is XXXXX XXXXX I'm a Real Estate litigation attorney. Thanks for your question.
If there is anything in writing that says the association is responsible for the deck replacement, then you have a right to rely on that written rule. If there is nothing in writing, it makes things a little more difficult, but if you can prove that the statement was made, you can claim that you had a right to rely on the representations made by the association, and therefore the association should cover the costs.
If the association refuses, you would likely have to sue and claim that you were frauduently induced to purchase the condo based on the misrepresentations made to you by the association regarding the deck replacement. If the alleged rule they found that says it is your responsibility was not presented to you or known about by the association before your purchase, then you would have a valid claim that the provision was not part of your purchase agreement.
You can claim that had you known of this issue, you may not have purchased the property, and that you certainly would have negotiated the price more to give you some ability to cover the costs of repair.
Thus, you have a valid claim, but it will likely take a lawsuit to fend off the association - - or at least a letter from a local attorney.