I accidentally added 2 quarts of 2-stroke oil directly into our 4-stroke 100HP Mercury motor. It was not mixed with the gas – it went directly into the motor. The good news (I think) is that there was already a fair amount of 4-stroke oil in the crankshaft – it was about half full already. Do I need to drain it all and replace with 4-stroke only, or can I just let it run its course and gradually add more 4-stroke to decrease the ratio? (I’m a newbie to boat maintenance, if you can’t tell... taking over for my husband - so go easy on my lack of knowledge!)