>>Is it the magnetic declination of the moons of Jupiter at work here?<<

Wrong, it's Mars deviating from Saturn, not Jupiter!!!! What were you
thinking. It happen once a year at the end of June.

Don't worry, everything will be OK next week.

ps.: if not ok next week, check the main shaft metal bevel gear inside the
odometer. It as a trendency to come loose, originaly it's press-fit. You
will have to remove this one and with small plier compress this one so it
will again be tight on the shaft.

Lol, Ben
http://www3.sympatico.ca/huotx/engine1.htm