why do you have the rotary valve cover resurfaced?

[cruisertom]

I have a major vacuum leak on my 94xp and read on another site about someone exchanging thier rotary valve cover for another from SBT? Do these go bad or leak? Just trying to find my vacuum leak.

 

[Dr Honda]

If the clearance is too high... the engine won't run properly. STB can cut the case to pull it back into spec.