The bearings can be replaced on the 610. There's a special tool for removing the bearing covers on either side, but if you can figure out a way to remove them without it, you'll then hammer the axle out from one side. Get the bearing off the axle, and then use a drift, bar stock or something suitable to drive the other bearing out of the bottom bracket. Might be easiest to do this without removing the entire unit from the bike -- but be careful!

Apparently the replacement bearings are a size thats not so readily available anymore, but I've never tried to get them. Might be easier to source a replacement off eBay -- they don't sell for an unreasonable amount. Good luck.