Raji, we use the 50 ml Cornings up to 25K RCF in our F13S-14x50cy rotor without leakage so it could be a batch specific problem with your Corning tubes. Try to talk to Piramoon or one their resellers (Thermo?) in your country if they have some batches of 50 ml tubes in stock that they can guarantee will not leak in your application.
http://www.piramoon.com/product_specs_hs.php?pid=50 Best regards, Martin
