This is fact: A gap may or MAY NOT go back in place perfectly,no matter how clean and careful you are with it. We had a Grizzly 16" lathe in the toolmaker's shop. I had to remove the gap to true up a 20" bandsaw wheel that had been welded. The gap would not quite go back perfectly,no matter what I did. The gap stuck up from the rest of the ways so that the carriage was deflected upwards some after replacing it. And,the gap was file hard. Fortunately,we soon got budget to get a better,larger lathe soon after that. The only cure would have been to try milling some off the bottom of the gap piece. But getting it parallel and just right would have been a tricky job. It would have had to be indicated all over to determine where,and how much metal would need to be milled off,and if it had to be milled at a small fraction of an angle. Then,it'd have to have been gotten into the mill just right. At worst,the whole bottom could have had about .015" milled off parallel,and shims put in under the gap piece as needed to take care of any taper. Careful use of an indicator could have gotten the ways of the gap back parallel. That would have worked,but would be sloppy machining.I have the same model lathe at home(bought the 2 together in 1986). I had a 24" swing job to do. Reluctantly,I removed the gap. Luckily,it went back into place perfectly flush with the rest of the ways.Apparently some stress can be relieved when these gaps are removed,letting them warp a small amount. So,good luck. Both these lathes were made in Taiwan,mind you. I couldn't swear to the castings being properly aged. They all do it in ovens these days,though.It is not a good thing to leave the gap out. Unless you have a lathe with an English type carriage(big carriage wheel on the right end instead of the left end),the gear runs off the rack before you can get all the way to the chuck. And,even worse for face plate work. You'd be 5 or 6 or more inches away at best. Closer with a chuck,but still not all the way to it AT ALL. I didn't measure it,but noticed it when I had the gap out of the 16" lathe at work. The English Myford lathes have no gap piece at all,but their carriage arrangement allows for the lathe to work any way. Their gaps are not very wide.Even if you could reach the chuck with a cutting tool,etc.,it is still not a good idea to have much of the carriage hanging out in mid air.I wrote this in a very offhand way,but you get the idea. And these are real experiences. Oh,yes,the temperature in the shop was constant. And I am a maniac for getting such things CLEAN. I was so happy that my own lathe fitted back perfectly!!!