I just bought a 5hp 2-str tohatsu (model M5B, serial 36977264) that had only been used for 4 hours and then let sit without being flushed of the saltwater. So I changed the gear oil, put in new oil drain gaskets and bolts, used it another 5 hours and then (for unrelated reasons) went to change the gear oil again and found it milky. <br /><br />So there's water leaking into the gearcase. I assumed there are only two ways for it to get in, once you eliminate the drain bolts: a) from the top, through the impeller, driveshaft and all that stuff, or b) from the prop shaft. I checked the top, everything looks new, gaskets are elastic, no cracking, no nothing, and also no trace of gear oil leaking out. So it must be the prop shaft, and I vaguely remember seeing oil on the prop when I took it out of the car to mount on the boat...<br /><br />The prop's off (actually fell off with all the mounting hardware -- sad story, I did not check the shear pin for corrosion), but I can't remove the metal ring that bolts onto the lower unit housing to see whether the seal around the prop shaft is intact. <br />I don't have the manual for this motor but my other manuals call this ring the "gearcase head", so I'm going to assume that's the right name; correct me if I'm wrong. This gearcase head is really pitted and corroded, and I don't see how to take it off to look behind it. Is there a way? <br />And is that the right thing to do to check for water leaking into the gearcase, in the first place?<br /><br />ps: if someone can deduce what year this motor is from the serial (36977264), I'd be curious to know.<br /><br />Thanks!