Originally Posted by
3Roch
Perhaps better than using water etc or a light to find a crack ( the crack could be full of crud).
When you have the BB open plug up any holes in the frame including other side of the BB, rig up a BB size plug on the air chuck on your air compressor, put some soap water over the suspect area and put some air pressure (don't need much) inside the frame. No bubbles= good, bubbles= bad
That might be tough sticking corks into both the downtube and top tube, but it's not a bad idea if the aforementioned tests come up inconclusive.
-Kurt