Old rivet from a previous repair. Note the grinding marks.
Old rivet ground away and removed.
New slider installed and rivet peened.
A couple of tips for re-installing the slider. Disassemble the slider before you peen the end. Give it a dip in some hot water to soften it, pry gently on the plastic clips and remove the rubber "spacers".
I cut a "X" in the rivet with a Dremel tool with a cutting wheel. This reduces the force needed to spread the rivet. Less chance for an "oops!". You can see the marks in the last picture. A small, shallow hole using a drill will work also.
Place a bit of metal stock (I use an old king pin) into a vise standing up. Try to use one which barely fits into the plastic of the slider. Seat it solidly in the vise. Don't try to hold it in place using only the clamping force of the vise jaws. It WILL slide and turn sideways!
Have a helper available to hold the regulator assembly. Use a center punch to begin the peen and finish with a good drift punch. Don't go crazy with the hammer selection. You don't need a three pound sledge but you also don't want to use some twelve ounce tack hammer.
Re-assemble the slider, slip the regulator into the door and feed the slider into the window rail before you line up the mounting studs. Use a synthetic lube on the track. Using a petroleum based lubricant will degrade the nylon slider and cause premature failure. Replace the vapor barrier. This will cut down on the amount of dust and grit attracted to the slider jaw and track.