Originally Posted by Mark Kelly

The BB you have in now is an older AC-H or the cheaper SC-S (the only diff is that -H is a hollow axle), you can tell by the six "dimples" in the NDS cup. These are sealed bearing units, as are the more modern parts. They are basically not repairable.

Get the cranks off and spin the axle with your fingers. If it turns smoothly, leave it alone and put the cranks back on. If it feels lumpy and rough, you'll need to replace it, I'd use the more modern Centaur part which will cost GBP 33 if you buy it from Wiggle or you could get a Token for about half that. Despite the price the Token units are quite good, they move the chainline out by 1mm but that shouldn't be too big a problem.