MOC3043 possible failure
For 5mA, the MOC.. datasheet says you have &lt; 1.2 V forward voltage.
That means (5-1.2) V = 3.8 V need to drop over R2.
3.8 V / 300 Ω = 13 mA
So, yeah, you're pushing about three times as much current through your LED as you should.