My truck is dropping out of gear at highway speed and seems to be getting worse. Doing a little research and have determined that it is quite possibly the spring inside the shifter box that is mounted to the steering column. I got another one with the trans and engine that I just picked up and have it apart to clean up. My question is regarding the spring and what clearances should I be looking for? Read a previous post which directed me to a seller for a rebuilt. There is not a whole lot in there to go wrong/replace but parts sourcing is probably the issue. Thoughts, ideas??

1955 Chevy 3100