my sp does the same, i tried the 12 o'clock crush washer/plug fix, but to no avail. i think one of the orings on one of the studs dried out, and is leaking under pressure...
I have also noticed some oil on
the right jug under the spark plug. It does not look like the head gasket is leaking but there is oil on the fins above it. When I pulled out the spark plug it had oil crud all over it. Any suggestions?