I went back to the bike and did what I should have done and finished the frame inspection. It was clean except on the bottom of the top tube. I found more of the same damage including a spot with a similar straight line through it. The spot was slightly soft when I applied pressure with my finger.

There were a number of 'spidery lines' and overall the damage is visually consistent with the CAAD10 that CliffordK linked to (thank you). I couldn't help but notice the CAAD10 appears to have the same Cannondale clear-coat over bare metal finish as my frame.

I'm the original owner; the bike has about 5,000 miles and has always been wiped after rain and stored properly. It seems odd that 4 areas of corrosion would occur on a single tube with none visible elsewhere on the bike.

I posted a couple more pics of the damage on the bottom of the top tube.

I'll mull this over for another day or so but as one poster pointed out there could be more extensive corrosion inside the tube.

Any other thoughts? Can't thank you enough for your thoughts and comments.

Brian