As far as I know there isn't any washer or bushing. The GP's thread in as they are. Only thng I can think of is that you cleaned out some of the carbon and it now the GP threads in deeper. As far as using an allen wrench, I would never stick anything without threads into something with theads as that would tend to flatten the threads. If you need to clean threads, always use a thread reamer.

__________________
DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012