Alright first- of late I've started to hear a crunchy/gritty noise coming from my rear wheel when pedaling or coasting. I think this means there's some kind of dirt in the bearings. It seems to be coming from the part of the wheel where the chain drives the cog. Correct me if this assumption of dirt is wrong. This is a Sturmey 3 Speed hub from 1974 by the way.
If that's right, then I figure the solution is to clean up and re-pack the bearings with fresh grease. How easy a process is this, and what procedure do you recommend? I've never done this before (though I've worked on other things quite a bit on this bike) and if it's a hard one then I can pass it off to my local shop. But I'd rather keep my money and get a little good work in if it's an easy one to do. Any thoughts?
Edit: this whole thing assumes that there actually is grease at work here. I always had the understanding that oil was used to lubricate the hub's inner workings, but that grease was used on the bearings in the drive train. If not, then please advise me on it.