980H leaking hyd oil into transmission

Hi

I have a customer with a 980H 16000hrs it got a full trans rebuild recently since it came back it's leaking 5 litres per shift from hydraulics to the transmission we swopped the pilot and secondary steering pumps with another machine we fitted a new primary steering pump this only leaves us the implement pump but it's not wet around the tell tale holeso I don't think swopping this will prove anything.Has anyone came across this before??