Re: 1976 evinrude 85 hp gearbox oil query
Put an appropriate sized drip tray under the outboard. Remove the drain screw (large slot screw, very bottom of lower unit), then proceed to remove the vent screw. Take note of any metal filings on magnet of drain screw. Also take note of colour of oil removed, especially first to drain. If it is a milky white colour there is water intrusion into the lower unit. Keep motor vertical and let drain. Be sure to use proper marine grade oil. I like the containers that allow for the screw on pump, much easier than the toothpaste type tubes. Attach pump hose to the drain hole, lower hole, and slowly pump the oil until you see it exit via the vent hole. Install vent screw, with new gasket (very important). Remove pump hose and install drain screw (with new washer). Clean up and you're done!
Off the top of my head, I believe it holds 28 ounces, but regardless, keep pumping until oil exits the vent hole.