If your gun has been working before and suddenly has developed symptoms as described, I really doubt your hammer assembly is the cause. Paint and tolerances don't just get thicker over time, and I'm sure you tried cleaning the assembly before posting.
Try taking apart your BBU assembly and checking your nozzle. Check for any cracks in the plastic and see if it glides back and forth on the piston head rubber without much resistance. If possible: try replacing both the piston head, rubber, and loading nozzle altogether - ensuring they are all the same brand for best results. Like the hopup rubber, the rubber on the piston head can swell over time with oil and cause excessive friction. If your nozzle is cracked, then it does not deliver enough gas to rack the slide backwards. Both these problems do display the symptom of "light strikes and little recoil action" as well as jams if your piston head rubber has been swelled up.
The above seems even more likely since you mentioned your mag is good for only 15 light shots - which probably indicates both "inefficiency" and "that its not actually light striking".
If the gun has never worked before and you have a heavier metal slide, try using either hi-flow valves or a WE magazine (that comes stock with hi-flow) as a temporary fix.