When I removed the old fuel filler neck I noticed some sort of seal on the underside where it screws to the body.  I'm guessing that this is to help prevent exhaust fumes from entering the cabin.  What should be used to help seal this when installing the new fuel filler neck?  See pictures for location I'm talking about.

 

 

I think I just used whatever sealant I had on the shelf at the time, it doesn't need strength, the screws are taking the weight so you just need to fill the air gaps. Nice clean undercarriage!  

1 hour ago, grannyknot said:

Nice clean undercarriage!  

Not my car unfortunately, pix were grabbed from the internet as examples.