My two geldings are always mutually grooming each other. Literally all the time! In summer, they ripped each others fly rugs from it, but now they are not rugged because they aren't getting bitten from insects.
But now there's another problem, they are ruining each other's manes by chewing on each other's crest, like where the mane starts.
The arab/belgian used to have this gorgeous think long blond mane, but its getting thinner and shorter. I groom them daily but that's as much as I can.
I think its great that they get along well enough to be mutually grooming each other...I just don't really want them destroying their manes.