I actually had slop in mine and it caused flutter, I had to pull the flap and add hysol to the flat wood inserts that are in the flap itself. When the hysol started to set I ran the drive rod through it to form it to the width of the metal drive rod. Only grinding on the rod I did was to round the very end of it so it wouldn't cut a channel in the flap guides.
Unfortunately every model they make is different, I would say its pretty normal to have to mod things to fit.