What was found
APU SMOKE: WE STARTED AN APU ON 5MILE FINAL. UPON LANDING AND TURNING OF THE RUNWAY THE COCKPIT AND THE CABIN FILLED WITH WHITE OILY SMOKE FROM AIR VENTS. . WE SHUT THE APU AND IT APEARS FOR THE SMOKE TO STOP INCREASING. WE QUICKLY TAXIED TO THE FBO AND DEPLANED PAX WITH NO OTHER ANOMALITIES. REMOVED AND REPLACE FAILED AIR CYCLE MACHINE. PERFORMED OPS CHECKS AND LEAK CHECKS NO ISSUES NOTED. ALL WORK DONE IAW CL350 MM REF. 21-52-13.