Leaking Waterman L'etalon

[Robb1980]

Rookie question - What would cause a converter/cartridge pen to leak at the grip? There is no obvious blockage and does not leak except when held in the writing position. I'm guessing this is a feed problem, but would appreciate any comments and suggestions on how to correct. It's a beautiful pen that has been in storage for a long time, was flushed, but began to leak as through the ink is backwashing into the barrel. Thanks in advance.

[jebib111]

When you flushed it did you pull the nib and feed?