Re: 1992 Mariner 15 HP outboard trouble
Is there an oily film on the powerhead itself - in particular, just put your finger up under the flywheel and give the top of the powerhead a wipe. The 6/8/9.9/15 horse powerheads are notorious for blowing two things - the upper main crank seal and the intake gasket (the one on the starboard side back near the plugs, not the one behind the carb).
Both conditions will make it seem like a 1.5 cylinder model which often leads (mistakenly) to carb repairs.
So check for the oil sheen (almost like the motor was "fogged") and if it's not present I would check out the intake gasket..
A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)