My Mercury 3.3 2-cycle has been trouble free for the 5 years that I have owned it. I am stymied by what has been a very routine task - changing the lower unit lube oil. This year I removed the upper and lower plugs and had a small amount of fresh-looking lube drain out - maybe a couple of ounces, with no evidence of contamination. When I tried to add new oil, only a couple of ounces would go in, and nothing came out of the top opening. When I removed the lubricant tube from the lower opening, the fresh oil gushed out, as if under pressure. Several more tries resulted in the same result. I then ran the motor for a few minutes - in the water and on my dinghy. Everything worked fine - shifted into gear, seemed to have normal power, etc. Tried adding more lube to the lower end with same result.