Custom Wood Deck Repair questions

Hi I am not used to forums, and i don't use social media so please forgive any etiquette mistakes on my part. I have a question about repairing an old custom deck and I am hoping someone can give me some good advice on how to move forward. I work in property management. I have done various forms of construction throughout my life , so I do have understanding on how things work so if answering you can do so without "breaking it down" to someone who is a weekend warrior. I have to do some repairs to an approx. 3O yr old custom deck. The deck was built with no screws, nails etc. All notched. The railings and hand rail that runs along the stairs is starting to flop away from the stairs. This is caused by aging and the fact that the hand railing itself is 16" wide 1O " thick and is 18' in length. Very heavy. The handrail has cracked lengthwise over the years, someone did a quick wood filler job, but did not address the structural aspect of the railing splitting. So now I have to repair the notches so they are good and tight, and I am hoping to find a way to fill crack, while gaining some structural integrity and shear strength. My thoughts on this are to, either drill notches and the use dowel {hardwood| to tighten along the base of the railings where they meet the stairs and where the handrailing meets the deck. The crack is the most troubling for me because i can wiggle both sides of crack so my estimate is 1-3 years and full split. I am thinking about spline lengthwise, filled with oak or maple, combined with wood glue maybe combine this with some hidden diagonal bracing / blocking under notches/joints . I know I could use L brackets screws etc. I am trying to keep the original look and feel of the custom job. but I have no experience with this kind of custom, joints/notches only wood work. I have also no experience with trying to repair such an old piece of wood as most of my jobs are typical hand railings you tear out and replace. I also should mention I live in Northern Canada so our winters can be hard, to top that off it is considered a snowbelt area so any repairs would need to be able to withstand the moisture, freezing temps and expanding throughout the winter Any and all suggestions would be greatly appreciated. Thank you very much

 

If the boards feel soft or spongy, I usually poke around with a screwdriver to see how far the rot goes, then swap out anything that crumbles. Warped or cracked boards can often be saved with sanding, but structural posts or joists are better replaced. If you get stuck or want a second set of eyes, I’ve found contacting https://harbordeckandfence.com handy for figuring out what’s worth fixing and what’s better to swap out.