They often get gummed up because people put in the wrong oil... 3 in 1 is terrible as it is vegetable based and will turn to sludge whereas good old 10W30 or a heavier single weight oil will work just fine.
I always use synthetic as I often find myself riding in much colder weather and also use this is the bb of bikes that have oil fillers... it makes for a really smooth running bike as the oil flushes out any contaminants whereas grease traps them.
My Lenton is a full oiler as it's hubs are also ported for oil and it has to be one of the smoothest running bikes I have ever ridden... the Sports has an oil port in the bb.