A Makergear forum discussion on PETG hair and the prevention thereof prompted me to take a look at the silicone coating I’d applied to the nozzle:
That was ten months ago. This is now:
The camera sees the nozzle in a mirror laid flat on the platform, making the image less crisp than a direct view.
So the silicone seems a bit worn around the tip, has acquired a few firmly adhered globs, and definitely isn’t as shiny.
Rather than (try to) peel it off and reapply a new coating, I picked off the globs, cleaned around the nozzle, and slobbered a thin layer atop the existing silicone:
Extruding a few millimeters of filament pushed the film off the nozzle opening and it now works as well as it ever did.
The Smell of Molten Projects in the Morning 
How many spools of filament does a nozzle last?
After 4 kg of PETG the nozzle is still in fine shape!
Because I use only a single plastic, the nozzle doesn’t get clogged and doesn’t need (interior) cleaning, which means I’m not reaming it with wire or drills. Steel can’t possibly be good in a tiny brass hole, but maybe I’m just a fussbudget about such things.
Folks report carbon fiber filaments definitely erode brass nozzles like crazy, hence hardened or stainless steel nozzles have become a thing.
E3D are now offering secret sauce nozzles, if memory serves they are hardened tool steel, plated with something even harder and nanocoated with a non stick layer of some unobtanium stuff. I’d love to try one, but realistically I don’t need it and they charge 27GPB which is a bit crazy. Sanjay claims it’s possible to get a very flat top layer by ironing the print with the nozzle (no extrusion) since plastic will not stick to it
“Ironing the print” … that’s a technique I never imagined.
Seems like an up-armored nozzle solves many problems I’m glad I don’t have!