Mercedes G 270 CDI, 400 CDI engine and electrics

Hello, I’ve been looking for a Mercedes G 300 TD for a long time, but unfortunately this is more difficult than I imagined. It’s impossible to get a 5-door with the engine and the equipment and at an acceptable price. Now I have become friends with buying a 270 CDI or 400 CDI. Since you read many horror stories in the forums I have the following question. Are all in principle bad, so problems with engine, gearbox and electrics, or just the first of them? Can you say that the G’s are more reliable from a certain month and year onwards than the ones before? Furthermore, I had read somewhere that the 400 CDI had changed the engine from a certain date on and this can be seen from the engine cover (photos). Is that true and what has been modified? Thanks for your answers and if one has to sell one or if one knows who sells one please report one. Thank you in advance. Claude