04 Mercury 60 exhaust Lowe unit

[astron]

Boat been stored 10 mos. Cranked readily ran approx. 10 miles; now, happen to notice that while at idle that there was light greyish "cloud" emanating from the upper vents just above the horizontal plate in lower unit. Boat ran great, no unusual sounds and housing was not the least bit warm immediately upon trailerng. No apparent oil or residue seen and only could smell very slight scent which I think smelled like tcw3 oil, not familiar with gear oil smell though. Possible seal leak? Insect critters crawled thru the vents made a nest,mud daubers? Or is this really nothing, just hadn't noticed it ever doing that. Seals are obviously much cheaper than blowing a lower unit. 100 an hour labor depresses me......