capping problem Mutoh VJ1604-1614

Hello I am new to the forums, but I saw the need for help in this way, I sell some parts for these machines, I am new to the business, but I had a problem with two capping for different customers to purchase .

1 - When changing the capping works great on cleaning the unit, but soon begins to fail and there is good suction ink to clean the print head, then you have to make pressure on the underside of the capping for I can do a good suction, I want to clarify that in one case the cleaning unit is new. I have a person who is technical but could not reach out to the problem, so I go to the help of this forum to see if someone has this happened the same.

Thanks for your kind help.

Greetings.