Is it possible that some Guzzi engines do not use an o ring between the phase sensor and the block? I was able to get to the phase sensor rather easily after removing the left header pipe, and what appears to be a hose that serves the crankcase ventilation system. I have the sensor and shim stack removed, but I see no sign of an old o ring. I have a new o ring, but since the shim stack must be critical to the air gap, it seems like the o ring would throw that completely off if it was mashed between the shim stack and the engine block. And it doesn't appear that the o ring fits inside the hole in the shim stack.
What am I missing here?
UPDATE: Forget the question. There was still one shim stuck to the engine block, and the o ring was where it was supposed to be .... in the place machined for it, under the shim. This is one fiddly way of attempting to seal the sensor. 3Bond to the rescue!