Now that you posted some pics it seems to me that the mech is apparently CAL designed made by Matsuschita and perhaps used by them also. I think the Acurus ACD11 and some Adcom uses that mech also....
Can you see any number of the back of the tray?
One thing i'd notice in one of the pics concerning the disc motor: Bearing wear causes serious tracking problems and I often find that the disc motor wears before the laser head. Maybe you could replace it...
But first do what Sam says. If it works, great. If not replace with a new complete assembly. You should make sure the disc motor is changed as well. The complete assembly assures you that the disc table height is correct.
Without the manual you shouldn't replace mech parts because you may need to do some adjustments...Sometimes the laser heads are adjusted to a standard at the factory, other times....

Maybe you can find something here:
http://www.dalbani.co.uk/index.phphttp://www.wescomponents.com/Note:
If you see that you cannot find what causes the problem in your great cdp you should try to contact these guys, also they have spare parts from CAL :
http://www.approvedaudioservice.com/Hope it helps.