Also the white 113 number seems to be a little bit different for both tanks. The one of posts #91,97 has that number moved more forward and painted with thicker font.
It's quite difficult to recognize. Initailly I had been thinking that was the canvas cover used for protection of the barrel tip while moving on the dusty roads or a muddy ground ones. But later I thought it could have been the LB-1 gun that had a muzzle brake instead of the fume extractor. But I'm not sure because I haven't heard about T-54 model 51 with the gun fitted.