The idea behind adding oil to an old engine that is new to you is to prove to yourself that the injection system is working. If you go this route, use a 6 gallon tank with a 50:1 mix and mark the engine oil tank AND the remote tank. Run the motor at speed for a while then check the marks on the oil tanks. If they show the oil level going down then that means the oil system is working as long as there isn't a huge mess under the cowling. Once the system has been verified as working, switch to the main tank of straight gas.Refer to the ORM manual for the proper setup of the injection pump to ensure the proper ratio if that is a concern..As Capt Matt said DO NOT over oil the motor. A gallon or two of mix is ok, but full time will lead to heinousness in the plugs, gummed up rings, and depending on the injection system to much crap in the carbs and or an eventual boogerd up O2 sensor...Best thing to do of is check the lines carefully. Tug on them gently, but like you mean it.. I had one crack on an outboard that sat out the season. Only way I discovered it before disaster struck was I noticed a mess dripping down the port side of the motor as she ran on muffs during fall pickling. A little tugging later I found the supply line from the oil pump into the fuel pump was completely split....
Back to oil injection. The Yamaha 115 and 130 oil injection system and components are noted for reliability in these parts.