Whirlpool F/F Leaking RSB33

I have been to an American F/F leaking it would seem to be on defrost as customer finds floor wet in the morning, Checked all hoses but very little water in evap tray so it is missing it, took flap of end and extended it into tray and left on test still leaking.

I feel water is leaking out through the insulation has anyone had this prob if so how do you over come it!

I work on other makes but have no knowledge of this one, how do you activate the defrost cycle

I have also poured lots of water down through the defrost tube no leak.

Thanks Kirk