Was it a solid carbide bit, or a steel shank with carbide brazed onto it? Your feedrate and DOC seem reasonable, but I'd run that at full speed (24K RPM) next time. I know it's noisier, but you'll get better results running it faster, and less load on the tool.
If I notice any light surface rust, I use steel wool and WD-40 to clean them up. A light coat of WD-40 seems to help keep the rust at bay during the summer months. I wouldn't think that mild rust or even pitting would be enough to cause a stress-riser type failure, but I really couldn't say.
I do have a couple of PC892 series routers. The first two ran very cool. When I bought the third one, it ran hot right out of the box. I contacted tech support and they told me that they had recently changed the bearings and that the router would run hot until it was broken in. It seemed odd to me, but sure enough, it's running very cool now. I would estimate this was after 50-100 hours of use, but I wasn't keeping track.