ucapajr

Hello all, I'm trying to fix my dead C3 2006 Senso-drive stop-start petrol. It came up with "Stop start faulty" a few days ago and has not started since. I changed the battery, still the fault. Checked the ECU for fault codes, none. I took off the aux belt to see the starter motor working and it trying the start it did cause the motor to turn, only slowly and jerky, not lasting more than 1/2 second. After one or two attempts at turning the engine over like this the start motor would not turn at all. Returning an hour later and I could repeat with the starter motor turning slowly/jerkily.I have take then the starter motor out and I think its blown, but I have no way of testing this here. Can anyone give any advise on what the fault could be? Having done some research it could be that the ECU thinks it should start the engine as if its stopped at the traffic lights and only give the engine a little kick, expecting it to start almost immediately. On the other hand it could be the stop-start alternator. I have looked for the second hand alternator to fit a stop-start and I can not find any, at all! I can find new one's at £600 for euro car parts. Ouch! Any help please?