Spraying after their boy ops

[Sooty]

Hi I have two lovely boy brother house rabbits called Sooty and Sweep. They live in a large conservatory family room. I have never had a pet before let alone rabbits. I committed myself to giving them the best life I could give them because I didn't like where they were living before. I had to split them up after a fight, until 6 wks post op. Even when they were separated they have been side by side. I was really lucky they bonded back together especially because they are both male. It would have been impossible to have two house rabbits that weren't bonded as one would have had to go in a cage which I really don't want. They have been back together 9 weeks and its lovely to see them mirroring each others behaviour, cuddling up and grooming. One of the brothers is a lot smaller, the vet thinks because he was the runt of the litter. The smaller rabbit (Sweep) still keeps spraying usually his brother, and I don't know if its still his hormones, or if its a sign of aggression or if its because he loves him or is bonding such a long process its part of that. Does anybody know what the reason is likely to be and is there anything I can do to help stop it? I dearly love my babies but I spend so much time cleaning. I clean with lemon and white vineger which does a good job but its far from ideal having urine sprayed. Any advice or insight into his behaviour would be appreciated.