With age the seal can degrade and allow fluid to get into the connection. This can cause erratic transmission operation, possible codes, and even force the transmission to go into limp mode.
This is an easy to install fix if fluid is present in your connection.
FITMENT:
Chevy GMC 2500 3500 Allison 1000 Transmission, (6.6L V8 Duramax Diesel LB7, LLY, LMM LML, L5P)