I've recently purchased a used 2005 G35 Coupe(manual trans) with 56,000 miles on it. When I bought the car it had just had the belts replaced and oil change. The previous owner had used Mobil1 5w-30 motor oil with the Mobil1 filters. I am looking to do some regular maintenance since the dealer records show he has never had the rear diff changed or trans fluid. I am nearing 60,000 miles and looking to change the Mobil1 for Castrol 5w-30 (from what I read it looks like a better oil than M1 and is easier to find than GC). I am also looking to change the spark plugs(check for known oil issue, warranty runs up in two months lol)

So with that said my questions are
1. What oil filter should I used? (m1?)
2. Castrol Edge vs Castrol Syntec (both 5w-30 and about $0.50 quart diff, I am looking at running between 4k-5k between changes with 50/50 split city hw)
3. What transmission fluid does everyone recommend(in general)/How hard is it to change (I have access to a car lift and garage)
4. What rear differential fluid should I use?

Thanks in advance, seems to be lots of knowledgeable people on this forum, even if you don't have direct answers maybe you can point me to the proper posts that answer them!

 

I use OEM Nissan oil filter

Castrol Edge but still go 3k between changes.

For the transmission and differential I use BG SynchShift II and Ultra Guard. I have a 6MT transmission.