Debating on a few options for how to seal drill holes for a Mazdaspeed style wing I will install.
I have a preventative rust treatment spray for bodywork that I will treat the steal with first.
But then what do people use to seal it?
There is seam sealer
​​​​​​silicone
And an option I just thought of, windshield molding sealer.

What has the longest lasting protection?

Edit: just realized I put this in the general section, ughf. Are mods able to move it?

 

Some Rust-Oleum and a good gasket has kept my hatch holes pretty rust free for the 2 or 3 years its been on there so far, but I think garage parking has been doing most of that work. I've seen people drill the holes, then fill the holes with resin and drill the resin again after.

 

This was one of the biggest debates I had for over a decade or so. At first I wanted to move to the updated 99 spec spoiler. At the time I thought the Mazdaspeed wings weren’t adjustable. I knew the gtc version had some adjustment but something didn’t make it sit right with me. Something was off.
I found out if I were to move to the spoiler though, I would leave 2 holes exposed. I knew to get them properly taken care of, I’d have to remove the hatch and get the holes welded. Apart from getting the entire thing repainted to make sure it looks as if it never happened.
So I held off. Until I found out the R spec wing had full adjustment and it looked better than the GTC version. I also managed to find a later hatch that came factory tinted (I really hate aftermarket film tint. Either get the glass itself tinted, or live without it ).
So I finally found a 2001 hatch, removed the rear wiper (I personally don’t find it necessary to have such a thing, plus my 94 never came with it), and found an R spec wing.
Sent the hatch to get properly welded up with all those exposed holes except for the ones that support the wing. Fun tidbit, the later hatches all come with the rear spoiler which has all the proper holes drilled out already. The wing only needs the inner holes and they line up perfectly.
Looks completely factory now.

 

I thought about the same question myself.

I might get a separate hatch with the spoiler installed someday and keep mine hole-free.

 

I also have considered getting a separate hatch, but I’ve decided to drill and fill my existing hatch.
I considered silicone or other sealer, but I’m planning on going the factory route and using a thin foam gasket. If Mazda was comfortable using it and being responsible for warranty issues, I feel comfortable doing the same.

 

I'd like to use one in addition to. Is there a PN?

 

Silicone may provide a good initial seal, but it can deteriorate due to weathering, vibration, or prolonged exposure to moisture. It also tends to peel off over time if it is not applied properly or if the surface is not prepared properly.

 

I think im going to put the metal treatment on, brush on some 2 part primer, 2 part base coat, 2 part clear, then goop it with windshield sealant. Should be bulletproof.