Have an 09 FLHT,
I am changing my polished outer primary cover for a chromed one.
My question is how much fluid will I need. The manuel say 38 oz of drain & fill & 45oz for install. (numbers may not be correct, don't have manuel with me).
How much primary fluid do I need to add with new outer cover ?

 

With the bike upright level (put a wood block under the jiffy) fill the primary to the bottom of the clutch hub so the chain is just submerged in the oil and will sling it all around. Do not overfill.

 

The numbers indicated (if accurate to the manual specs) would be the ones to go with. In your case since you are changing the primary you would want to go with the higher "install" quantity since by removing the cover you have absolutely drained all of the oil out of the primary.

The lower number associated with the drain and fill process identifies that not all of the oil gets drained when servicing the bike.

 

Fill to black ring in pic...Crash