250F Another 2004 KX250F Project/Build

Got the seal kit and a new spring, and ready to reseal this shock.
Question is - what oil goes in it?
Manual says SAE 5W or Bel-Ray SE2 #40, but I'm unfamiliar with either of these, and dont think either of them are available locally.
Is there an equivalent I can use?
Something that is readily available locally?
I have some fork oil, but I'm guessing thats not the same stuff...???
What the weight of your fork oil?
do you have a localshop that is going to charge the nitrogen? Mine was pretty brave(stupid) to pump mine up seeing as I was the one who rebuilt the shock.:sorry:
I cant find the fork oil, but I think its 10 and 15.
BUT, I just found a liter of Belray HVI Racing 5w suspension fluid that I didn't know I had.
Yes, I have a shop to fill the nitrogen.
Maybe a dumb question -
Why nitrogen for the shock?
Are there any other gases that would also work? Acetylene, argon, helium?