Yes, it is secondhand, I got it from a fellow APUGer. I transported it back home by car and although we did our best to cushion it, there may have been some jolts on the way. When I got it home I just span the dails noticed the colour shifts and thought all was good. B&W prints were fine and colour was easy enough to balance. I've tried printing three films, all of which have high filter pack values:

Superia 800: 100M/90Y
Pro 800Z: 100M/105Y
Pro 400H: 105M/105Y

It looks increasingly likely that something may have got dislodged on the journey home and changing the lamp last week shifted things back into place. But I'll take a good look inside the head this week and check for anything obviously out of place.