An out of round hole for the throttle shaft will not cause a leak, but that is where a leak will usually show up at. Wrenchbender explained the cause of the leak. However, if you do have an out of round hole, it will be a source of a vacuum leak and performance will be improved by fixing them. I use a small hole gauge to measure the bore like I use for measuring valve guides. The bore will be egg shaped instead of bell mouthed like a valve guide. I ream them out to the size bushing I happen to have, install the bushing and then ream the hole to fit the shaft
