Purlin repair - Do I need to do anything?

Thanks for reply, would I get away with not supporting it? I've been up in the loft again today after fitting some new flashing to the chimney. I attacked it with a screw driver again and it only goes to roughly 1.5cm for a 6 inch span of the purlin not all the way across the top of the purlin either. Just want piece of mind really. As if the rot really doesn't go any deeper it is minuscule in comparison to the size of purlin if you get me.

I get no luck either as lost my job

Hi. does anyone know If I were to sister a length to it with bolts etc if i would need to support it? One side will be resting on the brickwork. Its just there is nothing to support it on ie: load bearing wall is in middle of loft. thanks