A surprising break

For a few days now my bicycle's headset seemed loose so this morning I got a crescent wrench to tighten the headset's locknut. That is when I discovered a chuck of my bicycle's frame was missing.

I have no idea how this piece got broken off - or when it happened.

This isn't my first bicycle frame that has worn out (actually my third), but the previous frames have been steel and they cracked then broke. This is my first aluminum frame. Apparently aluminum doesn't crack - it just breaks with no warning.

I can still ride the bicycle, and I was planning to replace this bicycle for a year now as the frame has over 37,000 miles on it and is a little over 13 years old, but I guess I should make the bicycle replacement a higher priority. Once I get the weeds sprayed, the house painted, etc., etc.