Just had the PTU, RDU and tranny fluids changed by the senior Ford mechanic. Waited for 2 weeks to have this guy become available at the dealer to work on my 2018 SHO . Very particular and thorough is his reputation He came out and met me after and totally confirmed what SHOdded said about changing these fluids after 5k or so break in period. Case in point there were slivers in the PTU and RDU . He said that even after the revisions over the past years to the PTU it still has issues and not doing regular maintenance is ridiculous . He services the local police cars and sees the effects . His thought is that Ford thinks it's easier to just replace them because of the labor required to service them .He went over work of removing the catalytic, heat shield . He gave me the 9 page instruction sheet on how to do it . Now that it is done he recommends doing it again at about 40k . Oddly the dealer provided a maintenance schedule from Ford for my VIN that said to change the PTU and RDU at various time and distance intervals. Of course that is contrary to the owners manual .