So I've owned a few of these, some which oscillate VERY early and others that oscillate much later. I now have one of these that oscillates later and not quite as heavily maybe. Does anybody know the actual physical difference between the two and why this happens. The date seems to have little bearing on this as I've owned two from '81 that act totally different... There are internal trimpots, will adjusting them get me back in oscillating heaven? What needs to be done/changed? Thanks!