Two things I thought I’d mention. Injectors are slightly different depending on MY. Think it changes with EGR so if you have that. Particularly 4th injector as connectors different and not ideal to butcher a new one.
Other thing is if you read on the back of the bottle of injector cleaner I usually found a whole bottle per tank is for a smaller vehicle, size on the P38 tank it’s bit weak I always used whole bottle to half a tank.

Mechanical injectors are more robust than these modern ones, I’m also with idea it is actually the glows/spills not actual injectors.

An old neighbour of mine used to put the injector cleaner in the fuel filter and pretty much shove it through neat! That was on an old Pug diesel.