Dear Clemente, Torsten and others, Some years ago I visited Antonio Longinelli's lab for an interlab calibration. He told me that I should use only one type (I think N, but I am not sure) of Apiezon grease, and don't use the thicker type grease because it reacts with the O-ring and deteoriates it during prolonged use. Here in my lab I just use Leybold Lithelen to lubricate O-rings. The e-mail address of professor Longinelli I know is [log in to unmask] Cheers, Attila Dr. Attila Demeny Laboratory for Geochemical Research Hungarian Academy of Sciences Budapest, Budaorsi ut 45, H-1112, Hungary tel/fax: 36-1-319-3145 e-mail: [log in to unmask]