My parents got my brother and I Brio trains around 1984. Over the years some of those pieces broke and were repaired. Some of them got additional shades of pigment added. They survived through seven kids and now my two kids. Well almost survived.
Today I repaired three pieces by adding pegs. I made the pegs by drilling a 3/8” hole in a wooden ball I bought from a craft store. Then I glued in a dowel from the hardware store. Next I sanded the tip flat. Then I sanded the circumference of the ball to give clearance on the sides. Then I pre-drilled the track portion and dry-fit the pegs measuring the amount I needed both in the track and for appropriate connection to the next track piece. I then cut the dowel to proper size. Finally I glued the peg in with wood glue.