I had a coolant leak that turned out to be a bad gasket. Coolant was leaking into the motor. I had the gasket replaced, and was told to change the oil after a few hundred miles. When I did, it turned out that there was a lot of oil in the coolant. Shouldn't the mechanic who changed the gasket noticed this?
If coolant is getting into the engine, then oil will be getting into the coolant. It's a 2-way street there. I'm really surprised he didn't mention it, since it's expected. However, normally after doing a gasket repair of that type they just automatically change your coolant and oil on the spot since it's contaminated.