You have no basis and should amend returns.
The problem is bigger than you may think. Recaptured depreciation is taxed at the ordinary tax rate, while capital gains on the sale (looking at SEC1250 gains here) are taxed at the capital gains tax rate. If you just recapture all depreciation, then your entire original cost basis in the property will be taxed at the ordinary tax rate, since that's what you will basically be recapturing.
While you can do that, it's going to cost you big time on the tax front.
