Re: rebuild it, get a new on or leave it alone?
Merc deliberately leaves exact numbers out of publications. Reason is variables, mostly amount of oil in the fuel mix.
The cylinder to cylinder tracking is important, and as others stated, you are in great shape.
The rattling you hear in F gear idle is "clutch dog rattle". It's the sliding clutch dog (that does the shifting for you) popping in and out (sliding over the teeth) of the rear of F gear.
Your 75 is a 2.3 gear box as is my 90. Being a 2.3 they swing a prop with a lot of pitch on a lighter boat. When you put a big SS prop on these babies, they can and some do rattle. I just put her in gear and get the rpm's up to about 1000 and it goes away. Or I could put a light prop (alum), or one with shallow pitch and do the same thing but I'm not.
Merc has published a brochure on it and it is not supposed to hurt anything. Besides every time you cut the throttle on your boat your engine rpm's drop below the prop rotational speed (screwing thru the water) and the dog is sliding over the gears. You just don't hear it.
What you might do, beins you asked if there is something useful you could do, is to add some Sea Foam to your fuel tank when you gas up. It will clean up your combustion chambers. Now if you want to do something productive, that will really help, is relative cheap, and easy to administer, do that. You will not be sorry. BTDT
Mark
