I'm not replacing, but will be adding.
At the present I have metal toerails/T-tracks that over lap my deck-to-hull joint. After almost 30 years she seems to seep a little on the windy/rainy days.
So my plan it to pull the metal, re-install the fasteners, fill and glass over it all. Then add a mahogany (1" X 2") water
board (toerail) with a new T-track on top, staggering the fasteners between the old ones.
This should give it new strength, keep'r water
tight and create a stronger base for the safety
line stanchions, if you know what I mean!
I plan to to laminate 3/8" wide X 3/4" tall strips with DAP® Weldwood Resorcinol Glue (waterproof & stronger then epoxy) the shape of the curvature of the hull
, then laminate another 1/4" on top of that horizontally and radius the top edges to fair it in.
I could lacquer or paint
the wood but I can glass over that too. I haven't decided yet.
The problem with teak is it's hard to glue and to keep lacquer or paint
Some pictures of your old rail would help! That would give us a better idea of your set up and how we can make suggestions.