Adding Valve Seals to a Two-Valve Guzzi
      I ordered mine from a local (automotive) engine rebuild shop. The seals I used are for a MoPar 426 hemi. I believe the dimensions are 5/16" (stem diameter) by 1/2" (guide OD) but due to CRS syndrome you'd better verify the second dimension yourself. They have a Viton body with a Teflon ring for the stem and steel clip around the guide area. Ideally the guide should be machined to accept the steel clip but they will stay on without the machining. I'd suggest machining the new guides before installation so you have the option later to add them.

         When I installed them on the LeMans’ intake stems the plugs
went from black (one side) to their normal light gray color all around.

         For more info check out:

The ones I used are closest in appearance to ones pictured at the far
left, bottom row of the first link.

Pete Serrino