Underseal ,Rust prevention. Is it worth it. ?

I would agree to this. My FJ had some corrosion under the bitumen.

I can't see any corrosion.

Roger

The Plug itself and on the edges of the hole.

So I did (and would) treat the Jimny underbody and all inside spaces with corrosion prevention. I used a fat (8kg) but there are various options.

The plug appears to be rubber, I still cant detect any corrosion and the only FJ I know of is made by Toyota!

Roger

In some European countries the Gen3 Jimny is known as the FJ, with the Gen4 being the GJ.

Sorry for my unclear writing or pictures. The rubber plug is what I exchanged the rusty metal caps with and a FJ is an Gen3.

The metal caps were rusty after 3 years and the location is above the fuel tank under the bituminous coating, so in a somewhat protected position.

And I thought that this was the original question - if there is corrosion under the bituminous coating.

What cannot be easily seen is that in the area of the body where the rusty metal cap contacted the body there was corrosion.