Thst is disappointing. I have no experience with the new production Western Electric 300b but owner feedback has been very positive. They also have a 5 year warranty which inspires confidence.
I have used the EML XLS in my Frankensteins MK II for about 7 or 8 years by now and they are excellent! Very rugged construction and undeniably reliable. They sound splendid in this amplifier. I believe that you will be very safe with either of these two tubes.
Charles