I have a female mutt and a male Lab. Both are the same age, almost 5. The female has a nightly grooming ritual where she tenderly but thoroughly cleans the male's ears. He seems to enjoy it, and just lies there with that glazed-over look on his face, smiling as if he was getting a good neck scratching.
My daughter (13) says the female does this every night because the she wishes she had a puppy to take care of. My daughter hever has forgiven me for getting the dogs "fixed," because she wishes we could have a houseful of puppies at all times.
The male never reciprocates. My daughter feels bad for the female dog and sometimes takes a tissue and wipes her ears out so the dog won't feel left out and uncared for, LOL.