From my experience it could need a stronger main spring and set up. Polishing unless you went crazy on it should only make it a cleaner break. By replacing the mainspring housing spring and the trigger/sear/grip safety spring that should make it lock the sear in to the trigger. I had a older 1911 do this when i first started tinkering with the triggers. Which gtanted you may have taken off more metal than you intended to but by replacing those two springs with a stiffer set you shoukd be able to keep the polished parts. You couod test this by bending the factory sear spring forward to cause more tension for testing but i would not recommended this as long term fix. The sear prong is the left side of the three part spring
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