I figure if any particular brand of diesel has an additive package with a slight weakness, then using one brand over time could result in eventual injector clogging, because whatever can build up that is not removed by a certain additive will continue to get worse.

From that perspective, changing brands regularly could prevent problems.

Alternatively, we need some good way of non-invasively measuring injector performance to be able to tell when cleaning is necessary. Can VAG-COM tell that???