A method for in-field improvement or repair of a stationary gas turbine is carried out by successive removal of the gas turbine discs including its multiplicity of blades (buckets) from the common drive shaft. The overlying ring of tip shoes (shroud) and gas feed nozzles (stationary buckets) are similarly sequentially removed. Each disc is axially and circumferentially index marked with respect to the common drive shaft prior to removal of a portion of the drive shaft and substitution of a dummy drive shaft. The dummy shaft in turn is similarly indexed to the turbine disc index marks. Such marking assures that the turbine discs may then be reassembled to the common drive shaft so that no field rebalancing of the common drive shaft, and its assembled air compressor stages, is required for vibration control. The tip shoes, including the labyrinth knife edge, are then replaced by recoated shoes for control of erosion resistance and progressive abradability of the edges to accommodate centrifugal and thermal expansion of the blade tips. Deposition of the abradable material on the blade tips or erosion of the blades is avoided by reducing the clearance between the tip shoe edges and the blade tips with such progressive hardness of the abradable material on the tip shoes. Such reduction greatly increases efficiency of the engine by enhance of power out put and reduced fuel consumption.