06 F90 4Stroke Oil Leak

I just took my boat in for the 20 hr service and then to the the lake. All was well, but I now notice a small amt of oil leaking from small rubber tube in back of motor. I believe its the exaust. We had a hard freeze, but water was well drained from motor and it starts and sounds fine. My dealer says it must be they put to much oil in and its correcting itself. Its probably leaked about 1/2 quart over past 3 weeks, but shows to still be full. Any truth to what the dealer is saying?

[boats.net]

The oil pan drain plug is located on back motor inside a rubber tube, need to make sure oil drain is not leaking.