Last big rain some water reach the back of the seat... classic 986 story... ok
But I have a new top, new ECU with waterproof case, drains were clear and functionals(tested them), etc..
But I found the issue (almost sure).
My foam drain tray liner is not in good shape, and was not well installed at some places... not under metal part... (perhaps a previous job) I fixed some hole and reinstall the foam properly under metal parts, but the main issue is show on the picture... I did not see it before... Then I was thinking of two options:
1) Put some silicon or Permatex and do a "dirty" job to seal as I can all hole and precisely the big one... and test if it works.
2) Change all foam drain tray liners. Need to remove the top frame (which I dont know how to yet...), and all top parts, clean everything and check under, then replace the foam.