I think they are talking about to much shaft clearance not end play. All of the carbs I have delt with has a built in factor to allow for so much air to pass between the shaft and the bore, but it sure is not .008 of a inch. More like .002-.003.
I don't quite understand why it wouldn't allow the blade to come back to the original place each time as long as the end play is not so great the butterfly is actually hitting inside of the bore. I always leave the spring in place,but unhook it to stop any additional load to the servo and remove's most of not all of the end play on my carbs. I'll toss a indicator on one of my 50's or 55 tomorrow and see what that has for shaft play. So far it has not been any problem for me. But again it is not a 30, I know the carbs are different and that may have a bearing on things.
I have rebushed gawd knows how many Quadra Jet carbs due to this very same thing, It wold be a simple matter of doing the same thing to the WT carb. There is also a di- electric grease that may fix the leakage also.