I don't know if you know this or NOT, but you are actually agreeing with the guy down under even though you think you are making a point.
You said in your not so clever rebuttal ..."many people had with the Perkins motor in a mulching app in the USA."...Ahhhhh, that's pretty much what the guy from down under said. He said teh engine is good the APPLICATION IS POOR.
So to answer your question THEY REDESIGNED THE APPLICATION.
......"He had lots of problems with over heating until he updated the location over the roof. he still had some problems with the radiator and cooler because he brush cuts low lying areas with bullrushes sometimes and the stuff is like cotton. He demoed the new PT100 forestry on Thursday and said the machine is the real deal. he told me that the machines reversible fan can be activated from inside the cab or it can operate on the automatic timer"
So to answer WHERE DID THE PERKINS ENGINE GO? So you are W-R-O-N-G they are NOT using something else. They are using P-E-R-K-I-N-S
Well it went in the TEREX 2012 Forestry Mulcher unit. Model Perkins 1104D-44T
http://www.terex.com/construction/en/idc03/groups/webcontent/@web/@con/documents/web_content/ucm03_023839.pdf