Here is the port after I removed it. The damaged adhesive lip is obvious and you can also see the section I cut out trying to get the cowl bracket to fit behind the firewall. Clearly this is in bad shape.
I used a heat gun set on low to soften the adhesive and removed it with a putty knife. Then I used a dremel with a spherical engraving bit to carve out the cracks and a sanding drum to bevel the edges.
I used 36 grit paper to roughen the edge of the area I cut out. I used aluminum tape to make the shape I cut out. I saved the pieces and after roughing their edges with 36 grit, I set them in place.
I mixed a batch of epoxy with some colloidal silica and 1/32" milled fiberglass. I wanted it to fill the cracks pretty well so added silica and fiberglass equally until the mixture was like syrup. I applied it with a popsicle stick. I also filled in the cracks on the adhesive rim. Since the part is unseen, I didn't bother sanding it after the epoxy set up.
Next I cut several thin strips from a 2" wide roll of 10 oz fiberglass. I bridged the gap in the adhesive rim with a piece of aluminum tape and placed it on a piece of wood for support. I laid in strips of fiberglass until it was a little above the gap. Since this isn't a cosmetic or load-bearing item, I didn't worry too much about whether the cloth pattern was cross hatched or whether the gape was completely filled with material. I just wanted something for the adhesive to cling to.
After everything set up, I used a straight edge and Sharpie to mark where to cut the excess fiberglass to ensure the vent port would fit. Then I used a dremel with 80 grit drum sander to smooth the adhesive side of the surface.
SUMMARY: I would rate this a 3 out of 10. Since this piece is tucked away behind the kick panel, all I was really doing was gluing everything back together. No need to be too precise or worry about the shape and smoothness of the finish. This would've been much more difficult without the pieces I cut out, but I had always intended on putting them back in so saved them.
During installation of the cowl vent flap, I thought it necessary to remove the vent port behind the kick panel. Obviously that wasn't the case and though it may have made the work easier, I damaged the port in the process of taking it out. Lucky for me this piece isn't seen so my novice skills at repairing fiberglass were not a concern.
Vent Port Repair