In a couple of weeks I'll be installing ext steering.
What is the best method to make sure I don't have any leaks?

I saw a post where the op was wanting to coat the exposed wood with some type of wood sealer in case the 4200 failed to seal.
Is this a good idea? Could it prevent the 4200 from sticking?

I'll be using 4200 under the bolt heads for sure, but not sure if it should be used inside the newly formed bolt holes.
If I drill the holes so the bolts will be a snug fit, It will scrape off any sealant I apply.

If I drill the holes for a loose fit, I can get a good seal around the bolt, but I risk the plate moving.

What abt using a countersink bit and just touching the bolt hole opening? That should make a small void where sealant would be trapped.

Should I just seal the whole plate?

I'm a bit OCD when it comes to drilling below the water line

Drill oversize holes. Glass or epoxy the holes shut. Re-drill to bolt size and use life seal on the outside and inside.

3m 5200 is bullet proof, you wont look back

Do not use 5200. If you use 5200 it will not come apart when it comes time to fix, paint or change something.

Like Black Baja said. Make sure you seal the holes properly. I have seen a transom completely destroyed and rotted by not sealing the bolts on an add on hydraulic steering system. The destruction took less than 5 years

I would use the 5200 for anything smallish like steering fittings below the waterline. While 5200 is pretty much permanent, it can be undone with little or no damage on the kinds of items you are sealing. IMO, I think its the best thing to use for this application.

You can use DeBond to remove 5200. It isnt pretty or fast, but it works.

4200 and 5200 are nearly identical. They seal equally well. The 5200 just has twice the adhesive strength.

That's how I got my k-plane off, worked well. Like you said wasn't fast, lots of plastic pry tools, numerous applications but didn't damage the gelcoat at all. I used 5200 to reinstall it too because the transom where the huge hole was cut looked like it did the day it was installed in the factory.

absolutely, i would rather use a little effort to remove a fitting than worry about a potential rooted transom. after all, if its below the waterline i would not want somthing to come off effortlessly. most threw hull and transom fittings recommend 5200 such as why most boats transom assemblies etc come sealed with 5200 from the factory. it is also removable as mentioned above, may take a little effort but it can absolutely be removed.