The only ill effect on the turbo would be the ATF isn't really very lubrious and it will affect the viscosity and wet-out characteristics of the oil.
This is an OLD mechanics trick that I feel has been replaced with a safer chemical solution with high detergent oils like Rislone. The high detergent oils do the same thing as the 'ATF trick' without significant risk to bearing surfaces or to the degree of potential damage to Viton or Buna-N seals. You can pick it up at any auto parts store.
As for MCCC, Mitsubishi Combustion Chamber Cleaner, it is really a mixture of Methlyene Chloride, Toluene, and Xylene. These solvents will attack carbon deposits and remove buildup on the dash of the pistons and the heads of the valves. Its good stuff, just impossible to get now that Methlyene Chloride can no longer be distributed openly.