Wet coat along the whole spine?

My feral Minou came out of his shelter this morning with his back all wet all along his spine. At first i thought he has recently gone roaming and rubbed himself on something wet. I reached in the shelter but all was dry.  I let him inside for an hour so his coat would dry off. Twelve hours later, after spending most of the day outside, his back is still wet. He has short hair but it's almost like his fur is parted in the middle and has been combed to the sides. 
I have petted him, and my touching his back makes his skin twitch each time. I have smelled my hand and is smells of nothing so i don't think it is car grease.
He"s had his second monthly dose of Revolution 5 days ago.
What could it be? It looks like excessive grooming but the times i have seen him today, i haven't seen anything abnormal grooming wise.

If he still looks wet it's probably oil of some kind. Rub a little cornstarch into it to soak up the oiliness. Well, try drying it first---if it really is wet, cornstarch would make a goopy mess .

Also, applying flea meds can leave a big greasy spot. . .but it's not usually all way down the back, unless that's how you applied it.

I applied it between the shoulder blades as direction.

His coat is not wet anymore, but there is still twitching when i pet his back. Perhaps it was grease and there is still some in there, but it really did not leave my hand oily when i pet him yesterday. Strange...
Perhaps he has spine pain and overgroomed.