Just finished changing out the water pump on my Mariner 90 HP. I purchased some lower leg oil from the marina, and I was given the Mercury Premium Lube oil. It says right on the bottle not to mix it with the Regular Merc Lube oil.....this new stuff is blue? Is this a synthetic oil? If so,I wonder if I should have flushed the leg of the residual gear oil before adding this "premium" stuff..what do you people think?<br /><br />James