Any court in which an action is brought to enjoin, reverse, or declare void the proceedings by which any improvement has been made or ordered to be made under sections 6117.01 to 6117.45, inclusive, or 6103.02 to 6103.30, inclusive, of the Revised Code, or to enjoin a collection of a tax or assessment levied for such purpose, or any part thereof, or to which appeal is taken under section 6117.09 of the Revised Code to declare the improvement unnecessary or to amend the boundaries of any assessment district, or to modify the tentative assessment prior to the construction of any improvement, if there is manifest error in such proceedings affecting the right of the plaintiff in such action, may set such proceedings aside as to him without affecting the rights or liabilities of the other parties in interest.

The court shall allow parol testimony that said improvement will be conducive to the public health, convenience, and welfare and that any steps required by law for an improvement have been substantially complied with, notwithstanding any errors or defects in any record required to be kept by any board or officer, and without finding error the court may correct any gross injustice in the assessment made by the board of county commissioners. The court on the final hearing shall make such order as it deems equitable, and order any tax or assessment levied against the plaintiff to remain on the duplicate for collection, or order it to be levied in whole or in part, or perpetually enjoin it or any part thereof, or if it has been paid under protest, order the whole or such part thereof as it deems proper to be refunded. The cost of such action shall be apportioned among the parties or paid out of the county treasury as the court directs.