I agree that no one has done the definitive 1st generation DMU yet. The gear change issue as you say is not ideal but I'm not sure if anyone has captured that Leyland engine sound perfectly yet either. Then, It wasn't until watching Train Simulator on YouTube that I realised a key sound that these DMUs have is the change of engine note when you change from neutral to 1st gear, just before it pulls away. No one has replicated this yet (as far as I'm aware). Listen out for it at 28 seconds in. I know the sound quality of TS is far greater than what a chip and even the best speaker could achieve, so put that to one side. It's the characteristics of the DMU I'd like Legoman/Howes/SWD or even Hornby to concentrate a little harder on. A little later on in the video, at 1 minute 33 sec listen out for the rasp of the 121 exhaust. Would love that feature to be looked into as well.
https://youtu.be/n1waPA4VTIc
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