How should I prepare a whole (already roasted) leg of lamb bone for stock? So, I already made the leg o lamb and have some set aside for stew after I make the broth.  I chopped the huge bone in half so it will fit in a lobster pot.  The question for me at this time is: will it help to roast the bone for half an hour pre-stock?  

I spent so long looking online with no specificity found on this question that I've grown impatient and already started roasting the bone at a lower heat than I might usually--only 325 F-- since I figure it couldn't hurt.  But I wonder if it's necessary/helpful since the bone has been roasted (albeit beneath the meat) for four hours already.

Also, there is a little meat still on the bone before roasting, but mostly connective tissue and stuff.  

Thanks for any tips about re-roasting leftover roasted meat bones!
It is good to roast the bone before using it for stock in order to get color on it. Color adds flavor, so it is worth it. Only the bone exposed in the oven in the original roasting will have gotten any color as the rest was covered in meat. Don't worry about cleaning it completely, a bit of meat here and there isn't going to hurt your stock.