Re: I finally got my KM, but...
I know my grommets did not fit all that well either. The steam/base grommet if removed and placed into the base is a perfect fit. However when you put it on the stem, it is a really snug fit once in the base. I could not get it in all the way and did not want to force it in. So just use gentle force and wiggle it into place.
When it comes to the grommets, I found that the provided hose grommet was too small for the hose. I ended up using the bowl grommet to get a seal for the Narbisch hose. Luckily I had another bowl grommet to use and was not out anything. I will end up ordering a Silicone batch as I hear those are more compressible then the standard rubber style.
Most of all, be careful and do not force anything. Good luck man.