Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.
At this point it is most likely residual oil however to be sure use a degreaser and clean the entire inside of the hull as that is the only way to remove it all. Next for the water you will always get some degree of water inside, that is just how they are and it comes from top side, if coming in otherwise then you will want see if water enters just sitting in water, has to be engine running or only when operating forward or backwards. You will then check where the water is coming from (requires visual inspection), some common areas are hoses, head/exhaust gaskets, carbon ring/seal, hull pump support/seal, anything that passes through the hull, head pipe plugs, exhaust clamps/rubber coupler overall exhaust.
I am just seeing if you still need assistance with this problem? The reason I ask is because I see that your question has not been answered sooner and I wanted to make sure if you still needed help.
In some cases a question may sit due to several different reasons. My objective that I wish is to make sure that if you still need help that I can at the very least reach out to you and attempt to help you.
At this time please feel free when you are ready to reply back to me and ask to continue working with me, another expert or if you no longer need help please just let me know exactly what you wish to do.