So the first thing you think is manufacturing defect ,,, the first
think i think of is
House settling,
Rotted structure,
Insuficent supports,
Improper install.

And Thats what they , Anyone will look for first. First get out a long
level check plumb, level , square, 1/8 out and there is your likely
culprit, btw 1/8 is all major Cos allow. so WTF if you are off take
the SOB to court, Small claim , The damage is only now evident.

But ,and a big one is House settling.

Also an improper install is not leaving
" Shift Room " to tight an install is bad. Reseach the cause first.
Cracks indicate Shifting. Seal problems are usualy Mnfg limitations
but can be caused by the other ideas mentioned. Either way even if they
were in business it wouldnt be as simple as you think.