Agree with Graham, it isn't worth trying to buy 2nd hand used B&O ones as they haven't been made for donkeys years and most of them are likely to fail shortly due to aging suspension.
Go to the sound smith website and order the SMMC4 which is far superior to the original B&O MMC4 IMO. You may have to wait up to a month for delivery as each cartrideg is hand made to order but well worth it
Don't be put off by the relatively high cost as it should last you years due to the ultra low tracking forces of these cartridges.
Chris.
The use of metaphors should be avoided like the plague. They're like a red rag to a bull to me.