Its good to hear that oscar dont have any bahavioural issues, you can do the things below and just check whether it works or not...
I am just telling what i do if i face similar situation....
1. As labrador always wants to please his master and you can take it as an advantage...
2. Try to buy some dog shaped toys (get the one made of rubber or plastic (consider that the toy should not harm ur dog)).
3. First observe that your oscar afraid of the dog toy or not.
4. You can also give treats to oscar whenever he tries to play with that toy.
5. Try to show mirror in front of oscar and observe that oscar fear of it or not.
6. If he fears, ignore him else try to please/pet him.
7. finally, you try to made some barking sound and observe that oscar tails folds in between hins hind legs or not.
8. If he afraid of barking sound, then ignore him else pet him.