Aluminum is not a good choice for front fenders, especially the softer alu-alloys. They tend to form as easily as they tend to develop fatigue cracks. I do not think that there is a single OEM that fits aluminum front fenders, not currently anyway. They either do steel (adding fork bracing) or plastic (reducing un-sprung weight) - ABS or carbon-fiber in case of the latter. The modders will use aluminum to spin rear huggers on bobbers but only steel for wrappers on raked front ends - life is tough up there with the wind rushing in.
The eBay Alu R18 Fender is probably a commercial-grade pressing (no standard or norm to comply with and no reputation to risk), and a pretty thin one too, without any reinforcing added across its brace-width (where it mounts to the forks). I'll opt for ABS instead, already proven on a zillion Suzondayamasaki's, and Ducati's, out there. The R18B/TC OEM Steel Fender does not look quite 'right' on the regular R18 or R18C, IMHO. There is just kind of too much of it, I cannot explain it any better. The DK Design(R) 'gladiator helmet' suits it much better and I bet its wide neck at the back keeps lots of debris off the oil cooler.
I will be fitting a 16" R18C front wheel on my regular R18FE. I have 21" front wheels on my Breakout and Cross Country but I have fallen totally out of love with the 19", or potentially a 21", front wheel on the R18. It simply has to be 16" with the fat 130/90 front tire. Again, only IMHO.
