I also forgot to add that all said was done assuming that this problem shows up with more than one tape having been tried? as a cassette which is jammed up internally will result in the problem mentioned, because as soon as the cassette goes in far enough to connect with the spindle splines if the drive detects a blockage it will eject the tape again.

This problem strongly suggests that the carriage metalwork has became slightly warped and is allowing the cassette (or its carriage) to strike another part of the mechanism as it loads, difficult as it is to see this, but have a good study at the bottom of the cassette carriage metalwork and especially the cross member that supports the tape, if this appears slight bent try "very slightly" straightening it, do not overdo it though as on some mechanisms the metalwork doesnt look perfectly straight anyway. There is always a slight element of hit and miss involved in these type of adjustments and very seldom rectified first time.