Thank you for this. Have the same leak. Inspection plate is clean and was thinking maybe the oil pan is seeping is up impressively high? This makes much more sense.
In theory you want it to read after the collector. How much it actually matters in terms of accuracy, I can’t say.
And yes, the extra heat at the blanking plate will likely shorten the life of the sensors drastically. It’s also not ideal to install them horizontally
Wouldn’t recommend installing the afr sensor in the egr plate. It will likely be less accurate and fail sooner. A foot or two past the turbo will give you good results
The rarity of the delica doesn’t matter so much as the model of transmission. There were probably only 2-4 that were offered on the L400. A good start would be mentioning if it’s a manual or an auto.