Same here. I use a vacuum fluid extractor with the smallest wand / hose inserted into the bottom of the gearcase through the fill port to remove the fluid. Then refill with 75-90 GL5 synthetic gear oil. I do this annually and consider it good practice.I’m not familiar with the gearbox you have but to change oil in gearboxes without a drain plug just put some tubing in through the fill hole and use a big syringe or a pump like what’s on liquid soap to just suck or pump the old stuff out. No lifting and no mess.