This is a sweet bike.
It IS a sweet bike, isn't it?
I used a 100cc syringe to put exactly 180cc of oil in the tranny. My understanding is that you do NOT fill to the bottom of the fill hole. Just put in the 0.2qt/180ml and leave it. And make sure to spin the rear wheel while draining to get all the old stuff out. Any 80w90 gear oil should be OK. Given the long service life, it might not be a bad idea to get expensive/synthetic. At least, that's what i usually do with the longer interval fluids. Not trying to start an oil thread here.
For the motor, I used Rotella 15w40 in the white jug. The manual calls for 15w40, and those Diesel oils are the best for the price. The Chevron Delo or Mobil 1 Delvac 1300 should be as good for the same price. Or you can pay for scooter-specific marketed oil. Again, not trying to start an oil thread here. Oh, and I found two places in two manuals for my ('07) P150 that called for different volumes of motor oil. One said 980ml, which overfills mine, and the other called for 800ml, which seems about right.
And if you can drain the oil without making a mess of the rear brake cable and/or centerstand, I'd like to know how.