If you have something to measure the thickness of the spacer with, then go buy a few 3mm flat washers (some say #4 washers, but I found that they do not fit down inside the bore in the piston valve, or slide whatever you call it without grinding them down, 3mm fit right in there.)  Stack up enough 3mm washers to equal the thickness of half the spacer (I found it was about 2-3 washers), or whatever thickness you want to try, and use this washer stack instead of the white spacer.

This way you are not modifying the white spacer, just in case you ever need it as a reference or something.

Good Luck..Joe

Yes, I have my spacer in.  Which is why I am glad I did not file it in half.  I was just trying to help CanadianSavage out with his question.  I found out the hard way that #4 washers have too large of a diameter, and that 3mm washers fit perfect.

The previous owner did do some damage to the stock pipe when removing it, but they put a mac pipe on and that is what I am running with now.

Thanks...Joe