Can't find 80w 90 in RP. Can I use 75w 90 RP? Also, is this application for the GK-13B (Titan Plus 250cc)? Any pics on the gearbox drain and refill or location tips?

I need more info on this for my CN250 powered GK-13/titan. It has a forward/reverse gear box, a CVT and the Engine crank case. I already know to use 10w30 in the engines crankcase. Now is the crankcase seperate from the transmission/CVT or do they share the same fluid? I'm definately going to get some heavier gear oil for the FWD/RVS box.

Is the oil strainer shown on page 1 of this thread the only oil filter for these engines or is there an actual filter somewhere, i have not really looked that hard yet