I was contemplating doing a write up for this, but didn't want to do it on my first attempt. If I ever do another ill do something in a lot more detail.
As for sealing the lights, I used window weld from Autozone. Appeared to be the same stuff that they were originally sealed with.
Maybe I missed the information I'm looking for, but this picture from the linked thread shows it pretty well. The black exterior trim/seal I'm wanting to repair looks like it's fixed to the headlight lens in the picture above. Are you replacing this material or using what came with the headlights?
On my headlights it almost looks like a heavy duty tape(?) secured with glue/silicone. After a number of years and weathering mine doesn't look too good up close as it is peeling up a little and feels like the material is overly hardened.
I have never replaced the weather strip rubber piece before. If it is a little loose then I normally use a few drops of super glue and glue it back into place.
These headlights can be retrofitted economically. They are easy to do and there are plenty of cheap parts out there to do it.
I did do some testing last year comparing a premium build to a economical build, and I did find there was some noticeable difference in the brightness, the spread of light, the pattern of the hotspots and the ease of installation. Perhaps not enough to merit the almost 3 times the cost - but the performance difference is very apparent when compared side by side. The looks however are almost identical.