Here's what to look for:



What you're looking at is (from below) the non-drive side, top stay where it joins to the main tube. The crack is just a hairline running along the edge of the weld, in what a metallurgist would call the "heat affected zone." My son is a PhD metallurgist and could explain it in detail, but the bottom line is that the heat from welding makes those spots inherently weaker and only proper heat-treating will restore the strength.

Optima's line is that these are just paint defects; but I could tell it was a crack because it opened when someone sat on the bike. This frame had similar cracks at all 4 stays. Probably about 10K miles on it.