Just bought our first family boat with a Mercury ELPTO 75. Bought it used and without an owners manual. For the life of me I can't figure out how to check the oil level. Don't see any oil level side gauges and when I open the square compartment to pour the oil into, there is an additional hole that looks like a dip stick might fit there???? No clue - currently the a warning alarm goes off and I add oil. Also, when reading other forums, if I'm at full throttle and only pulling 4k rpm, is my prop too large? Thanks