Originally Posted by
draitzer
One other potential issue - there's an O-ring seal at the front of the (non-removable) valve body, #2621 on the diagram. Usually this seal is okay, but occasionally it can leak. Replacing it is a nightmare both in removing and in wedging a new one into position. One gent I know made a tubular "hole saw" type cutter to carve out the old and a smooth-end tube to pound in the new.
I mention this only because it's a possible leak source after successful exhaust valve servicing.
Don R.