It has been bouncing around my memory that somewhere around 15-20 years ago I read an article about one of the cog railways using a cog system that was a unique design that either lacked a safety feature or redundancy in some form. I seem to remember that t became an issue when they wanted to purchase new equipment and the manufacturers refused to quote due to liability exposure. I thought it was the Mt Washington cog because they ended up building their own diesel powered locomotives, but it might have been M&PP. I have tried searching but to no success. Does this ring a bell with anyone? Regardless, replacing all the rack rails would be extremely expensive and you would do it all at once because new and worn gearing rarely play well together.