I have a 74 model Nautaline, with hydraulic steering.  My question is what type of hydraulic fluid is best to use in these type of systems.  I have a couple of bad lines, and when I replace them I know I will lose some fluid.  I don't know the particulars on this system if it matters, the reservoir is mounted on the transom, with an air pressure gauge.  I assume used to push fluid to the flybridge.  Also any advice on bleeding these type systems for air.  The fluid that is leaking now is red in color, but as to what it is I don't know.  Your help is appreciated. 

What brand of system do you have? Hynautic can use Dexron but some brands use water glycol (antifreeze).

Hynautic was bought out by SeaStar.

http://ww2.seastarsteering.com/INBOARD/inboard.htm
OLD HOUSEBOATER38973.6994560185

I'm not sure of the brand as of now, I have looked quickly on the reservoir and don't recall seeing a name but that doesn't mean it wasn't there.  I can see the reservoir and the block that the steering wheel on the flybridge attaches to as the flybridge is off.  If you have any other suggestions as where to look i'd appreciate it.  Thanks

Usually on the reservoir.