Well, if the injector tank is full and there are no air bubbles in the oil line then assume it works, and do not bother plugging the line.
As for the plug....... 2 stroke engines are notorious for using up plugs pretty quickly. It's not unusual to benefit from a new plug with as little as 20 hours use.
Get another plug as a spare so the next time it is hard starting, try the new plug first.
As for the noise, are you used to air-cooled 2 strokes? They tend to make lots of engine noise because there is no water jacket to dampen the sound, and the cooling fins act like a loudspeaker for the engine.
I expect given the age of the bike, the piston and rings are probably pretty worn and loose, so the noise is probably 'piston slap'. 2 stroke engines do not last as long as 4 strokes, so it may be time to remove and rebore the cylinder and install a new piston and rings. Unlike a car, this is an easy job on an air cooled bike.