Graham,
Whilst I do not recall the history of your AVANT issue, there were issues with tapes not ejecting correctly.
You did not say exactly how far the tape had got in the ejection process, but there were intermittent jamming of cassettes during eject for which B&O produced a fix.
The problem was the jamming of certain types of cassettes in the tape mechanism during eject and it was caused by an edge of the cassette or a misfitted label, which could catch on the lower part of the cassette lid and prevent the cassette from being ejected.
B&O produced a new cassette lid, which is fitted with two small round knobs on the lower part of the lid.