Hi Ras! When I do repairs or additions with putty (milliput, green stuff or magic sculpt) I always add a small post inside the parts. Bore a hole in both the tip of the new part and the part you want to add it upon, then glue a small wire post (from a paper clip) in the new part, then when the glue has set, glue the other end. Glue itself isn't enough, plus, it's hard to find a glue that holds on PM.
Hope this helps!
A.