Can't answer your question about how long the bags last or how to re-fill them but I must have had my Rab down bag for five years or so now and it's still fine.
The problem with down bags is that it's really not practical to wash them yourself so it's well worth using a cotton liner in the summer and a fleece liner in spring and autumn will make the bag a bit warmer as well as protecting it.
I haven't had my bag cleaned yet and it needs it but one way of keeping the bag nice for as long as possible is whenever there is a hot sunny day, to turn it inside out and put it on the line. This keeps it a lot fresher. The small tents get put on the line as well.
How old is it? It might be worth ringing Blacks and telling them of the problem. Like Rik I have a Rab one that has never leaked down, I've had it for about ten years now, still as good as it ever was. Is it leaking from the seams? I know when I had to repair a down jacket it leaked a bit of down from where I had stitched the patch.
I cant really answer your question re the leak in your bag..But last year I bought a duckdown filled ex army mummy type s/bag(to be used for fishing)Tag on it says manufactured in 1986..so 23yrs old and no sign of any leaks/feathers..nor loss of insulation..which leads me to think there might be some sort of fault in yours!! in the stitching or something...Could of course be that my bag has been stored in some army depot for years before I got it but when I got it home it was full of leaves and rubbish from some squaddies boots and ponged a bit..Hand cleaned inside and out left opened out on the washing line for a few days to air..and its like a new bag..I'd contact Blacks to discuss the problem re yours...
Jelboy.
------------- Campers of the storm,Into this world are born