I'm hopeful fellow members can help me with a problem. I purchased this mantel clock with an ST 120L movement. After installing a new mainspring (with the original specs), cleaning and oiling, I started it up on my test stand and noticed it would run only 9 hours before stopping even with a full wind. Restarting it several times (without rewinding) it would run anywhere from 4 hours to 45 minutes before stopping repeatedly. There was no consistency or pattern in where the clock would stop. My first thought was there was some drag in the time train. I completely disassembled the movement, inspected all pivots and holes but could not find anything obvious. Much against my better judgement, I installed a slightly stronger mainspring, and reassembled and oiled the movement, pallets and cams. I restarted it on the test stand and it ran for over 6 days before stopping. Restarting it (again not rewinding) it ran for another 29 hours before stopping. Further restarts cause the clock to go only for minutes now. But the mainspring still has a fair bit of tension on it when testing it with a key. I am convinced there is some undue source of drag in the gear train, as the originally specified mainspring should be able to keep the clock going. As a side note, the strike side works perfectly. I have heard these are finicky movements from other postings I've seen here. I'm looking for any input, or similar experiences, and of course any suggestions on what the problem might be. Again, I lean toward a bent pivot pin or something.