[AyeCandy]

I had a similar problem with my VDO tachs from my 2007 Tiara 3600.  Was told it could have been a problem with the ECM, but thought it was strange it started happening with bothering the port and starboard engines.  I ended up sending to Fort Lauderdale Tachometer for bench testing, they could not find a definite problem but ended up replacing an LCD hour display and "reflashed" the tachs(whatever that means).  Got them back within 14 days and installed them and they have been working great.  Sure better than trying to find a new compatible tach and then not have it match the other gauges on the dash.  Nope that belps!