Thank you for replying. He just licks it a lot when he is sitting still. I thought that he maybe needed worming as it was getting to that time. I gave him his worming tablet and that irritated him a lot for about 24hrs. He was stopping a lot to scratch/lick himself on walks. That has stopped now though.
My vet did say that it was normal for discharge, but it leaves a lot of marks on everything and she said the colour was concerning.
If it's an age thing do you think a trip to a bitch would help? Or will he need neutered? I'm hoping not the latter because he has never been a problem behaviour wise since he mateured.