The 1500 BPM-buttons for ESRF-EBS had suffered from un-expected UHV leakage problems that are now clearly identified as bulk defects in the steel used for BPM body. These defects were identified with the help of X-ray computed tomography (CT) performed at two ESRF beamlines dedicated to this technique. The CT scans allowed to correlate the existence of small (<10um) but long (>10mm) channels in the steel with the BPM button leaks. All 1500 BPM buttons were screened, and risky buttons could then be sorted out. This reduced the occurrence of leaks but not fully suppressed them, mainly due to the resolution of the CT scans limited to a minimum of 2 um. Therefore a non-destructive UHV leak-test for the buttons was developed at the ESRF and is now applied to each of the BPM buttons.