I am the author of "these windows do suck" I replaced my top 4 windows with Anderson 400 series. The Semco windows were rotted at the sill.
I pulled the old windows out. No sealant at all around the flange no tape at all.. just pulled the nails out and the window came out.
I had to replace the wood under the sills.. the framing on the house was rotted.
The Semco windows were wood meeting wood where the window meets the sill.
Seems like a bad design to begin with.
The new Andersen have the clad part of the sill meeting a clad part of the window.
I have 4 more to do ..All the semco blow air or are rotted. The rest will be replaced later this year.