Replace double glazed window unit

[Mill2000]

Double glazed window unit(non opener) has failed and has condensation internally.
I Removed internal beading and found window fitters never used any packers.
Removed sealed unit from double sided glazing tape and it appears there are no drain holes.
Is this correct?
Is the double sided glazing tape supposed to keep all of the water from entering which would indicate why there are no drain holes.
Window openers either side do have drain holes.

 

[crank39]

To answer all your points in order

1- Must always use packers, packers keep the unit up out of any water that might sit in the glazing channel
2- Must have drain holes in all glazed areas
3- Double sided tape is made of foam and thus allows a degree of water to soak through

Any water that soaks through the tape or through the corners where the tape is just butted together should be taken care of via drainage holes, packers are there to keep the unit out of the water whilst it drains, a unit that sits in water for even a short time will blow which is whats happened

 

[Mill2000]

The window was fitted by a professional window company about 16 years ago and one window has only recently become blown.
So I can only assume the the double glazing tape was doing its job for all this time but probably deteriorated which allowed water in and with no drain holes it damaged the unit.