Valve Guide Snapped

Bought my current 1300 in Dec 2012 & noticed when it ran there was a very slight "tick" from the top end at front of the motor. After doing 3000 miles over this summer, I have now took the bike off the road to carry our work over the winter including honing cylinders, new ring, valve stem oil seals & a few other updates.
Once I got inside the head & removed the valves, I found one of the exhaust valve guide tops had snapped off & was just sitting on the valve stem with the seal around it.
The bike had ran perfectly well all summer over the 3000 miles & the "tick" was only noticeable when the bike was revved really hard, which I dont do often.
with all the 1300's I have owned & worked on I have never came across this before & wondered if any other owners out there have had this problem before ?
A photo of the section of valve guide that snapped off below.
Pete

Its a testament to how bullet proof this valve train is. That is for your bike to run that well with just a "tick" at high RPM.

That will never happen with a bronze guide.