How do you re-attach them to the top plastic trim piece?

From the factory they are held by a few heavy staples and some heat deformed plastic rivets, neither of which really end up reusable (the rivet heads pop of if you mess with them, and the staples are too ridged to be unbent/bent).

I've thought about screws or rivets, but I'm a bit worried that they'd scratch the glass/crack the plastic.

 

Epoxy plastic weld where the factory did the melt rivet thing.

 

On my car where the plastic nubs were hidden I just drilled them out and
used pop rivvets to hold it all together.
No problems with scratching the glass.

 

Have you searched for plastic rivets, or coated rivets?

 

+1 for pop rivets, same here.

 

you guys using pop rivets, did you use backup washers?

 

Nope, still holding strong after multiple years.

 

I use heavy/thick staples, similar to the ones the factory used.... just that I'll use about 5 of them rather than the 1 or 2 that the factory used.

I'll set the weatherstrip in place then drill a few tiny holes thru it and the upper door trim so each staple will push right thru by hand, then fold the staples from the backside. Never had to re-visit that type of repair once completed.

 

Where did you get the heavy staples?

 

Any heavy staple will do. IIRC the last time I did this I got the staples from a large appliance box. ( they just happened to be perfect for the job ! ) The factory used some pretty strong staples and the original ones are not always easy to remove,..... without destroying the plastic anyway !

GM should have used staples along the whole strip rather then 'plastic-welding' the studs IMO.