At the time the
maximum refundable balance was £5, so I used the card(s) to get the
balance below that figure then handed them over at the ticket office
and got the £3 + outstanding balance in cash. No identity required
nor reasons given. A very straightforward and simple process.

Nice to hear.

I own an Oyster card for several years now. Sometimes I topped it up in
cash, sometimes with a credit-card. If I now wish to return the card,
what would be the result: "No Sir, you have used a credit-card in 2004,
so you won't get anything back"? Recredit it to the card (but my current
card is not the one I used back then)? Ask me to fill a form, send it in
by post and wait for a cheque?

Does anybody know the current procedure?