F50 Maintenance questions

2002 Infiniti Q45

I have about 85K miles and was thinking I should get some maintenance done. I've been looking into the transmission fluid change. I've read everyone recommends doing a flush rather then a drain and fill. Also that the fluid MUST be Nissan's Jmatic Fluid. Read the manual and it clearly says "JMATIC ONLY" or else void warranty. Even though my warranty already expired I think there must be a reason for them to recommend that only. Anyways how much do you guys think it will cost at the dealer? My manual says my car takes 10 5/8qt but flushing i think requires more fluid. I've been reading 12qt. Also price per qt seems to range from $6-9 and most saying its around $9 per qt. What kind of rear differential gear oil should I use? I have some Mobil-1 Synthetic gear oil left in my garage. Does anyone know if that's ok? Anyone recommend any type of anti freeze? This week I'll probably buy a few gallons of distilled water and some more coolant. I'll probably empty whatever I have left of my Royal Purple Purple Ice into the cooling system. I'll probably change the power steering fluid and brake fluid but is the steering fluid require Jmatic also? thanks for looking!

2002 Infiniti Q45 I have about 85K miles and was thinking I should get some maintenance done. I've been looking into the transmission fluid change. I've read everyone recommends doing a flush rather then a drain and fill. Also that the fluid MUST be Nissan's Jmatic Fluid. Read the manual and it clearly says "JMATIC ONLY" or else void warranty. Even though my warranty already expired I think there must be a reason for them to recommend that only. Anyways how much do you guys think it will cost at the dealer? My manual says my car takes 10 5/8qt but flushing i think requires more fluid. I've been reading 12qt. Also price per qt seems to range from $6-9 and most saying its around $9 per qt. What kind of rear differential gear oil should I use? I have some Mobil-1 Synthetic gear oil left in my garage. Does anyone know if that's ok? Anyone recommend any type of anti freeze? This week I'll probably buy a few gallons of distilled water and some more coolant. I'll probably empty whatever I have left of my Royal Purple Purple Ice into the cooling system. I'll probably change the power steering fluid and brake fluid but is the steering fluid require Jmatic also? thanks for looking!