Air/Oil Shock Advice

[fotorat1]

OK so this shock was making a god awful squeching noise so I have opened it up and drained of the black stinking filthy oil that was in it

I am going to give a good flush

do I need special oil for it?

 

[fotorat1]

also how will know how much oil to put in it!

 

[fotorat1]

https://www.youtube.com/watch?v=QINqqzLtkDI

this covers it nicely