The return from the start position, is a function of the ignition switch, not the key cylinder. If you have to sand down the ignition cylinder just to make it work, then it was casted out of round, and there is nothing that you can do about that. I would suggest that you find a replacement, preferably a NOS unit, and have it "keyed" to your key. This is a common problem of a part not fitting or working like an original, since quality control isn't adhered to when parts are made by the lowest bidder in some far away country. I would always rather purchase used OEM parts, than use reproduction parts. Most reproduction parts from the far East are junk, in my opinion. I am guessing that since you replaced the original with a reproduction, that you might still have the original? If so, take it to a locksmith, along with your new key, and have new tumblers installed.