I can hardly wait to see!
I hope he will be encouraged to share some photos of what he has done with us! A surveyor, huh? THAT says a lot about the Ariel! And the surveyor!
The rub rail has probably been off a couple of times to plug the holes. 338 had blobs of silicone goop and smears. Another telltale were size larger screws and (always) slightly out of sinc extra holes.
If the s.s. is in good shape and worth saving then a restoration move is in order. Nothing will stick to where silicone has gone befor. I really hope you don't find any under the rail. I used a Dremel tool with tiny carbide abrasive wheels to clean the seam. Watch it, you can cut thru tghe tabbing inside. When you start, check from the inside that you are not cutting thru! On 338, paint had been sprayed up into the cove of the toerail, so adding more frp inside is extreme. Silicone has to be mechanically removed.
I think C'pete did a renewal on his Commander and added a layer of glass on the outside. You have to look for that. That is what you are looking at if you find a really bad seam and have to radically grind out bad glass and stuff. Hopefully a 5200 solution is the way to go for you. It has been done. Consider using the adhesive in a careful taped off stripe and then applying the rail dry or with a smear of polysulfide so it can be taken off again. Consider 5200 structural and sulfide bedding compound. If your seam is in really good shape you might go with all sulfide.
The thing is, if you are carefully going to put the rubrail back, you'll be using the same holes. They were never a good place for fasteners. You can't go with a size larger OR a size longer to get more purchase. So, if I was stuck with the same screws in the same holes, I would spend some serious prep time creating a new back for the screws with epoxy, cabosil, and glass powder in an attempt to produce something for the threads to grab. IE filling the seam and holes. That is my opinion. I don't think rubber will hold as good.
A wham bam thankya mam fix would glue the rail back on with 5200 and let the next skipper do restoration. Next time it would probably have to be done because the rail would be destroyed taking it off.
You will notice that nearly the whole length of the molded toerail doesn't follow the curve of the hull. The seam stands furthest out and can therefor be easily changed by a frisky makita. You don't want to change the profile of the joint because the butt joined hull/deck laminates are pretty skinny here.
1/2" s.s rubrail is available at a price, but you almost would have to get a shop to drill and countersink the holes. IE to place holes where the old holes aren't. Nothing wrong with a nice wood rail. Might allow extra frp over the seam. A concave surface on the mating side of the rail could accomadate some additions and make a nice gasket of sulfide over the seam. Seems to me Mr Griffith would be good to ask, too!!!
Oh, and on 338 the seam across the transome was filled and glued pretty well at the factory. The rail had to be prebent to get it on. If it is in good condition, maybe just leave it, leaks here are not getting in to the cabin sole, but that is open to discussion!