Mark under my dogs eye

My labrador has had a mark under his eye probably since March. I initially though that it was due to trauma (like a scratch). However, it hasn't gone away. It hasn't increased in size. He suffers from allergies and his skin is commonly more itchy this time of the year. In March he had a mast cell tumor removed on his back leg with a good prognosis and clear margins. I'm a little paranoid now that the mark under his eye might be a mast cell tumor but I'm not sure if I'm over reacting?! If I was to go down the route of checking it would involve him having another anaesthetic to do a punch biopsy which I'm in two minds about as it might not be a mast cell tumor! It hasn't increased in size and doesn't feel particularly "lumpy" it does look inflamed. I've attached some pictures. I'd appreciate any advice! 

Hi, i was wondering if you ever got an answer or ever went to the vet? as my dog has something very similar, and for similar issues of scratching, i havnt been to the vets yet as i’m trying to see if it goes down, was just wondering if you had any answers