Re: fuel injector cleaner (Dieder)
Haven't bought any Techron, Gunk or any retail brand, yet. Actually, I've only added cleaner to the BMW, mostly because I found a place that carries the Bimmer logo stuff for $2/bottle.
I was thinking of trying that stuff in the GTI, since it's cheap and meant for some kind of German car, back in the age of mechanical injection.
Anyway, once an oil change, the tank that'll be finished prior to the change, sounds like good advice in general. Of course, oil almost always has some undesirable stuff in it, that's why people in the northeast change oil prior to winter shutdown. The more important lesson there is to change the oil regularly.