Change fork oil

Drain the fluid and measure it, the drain plugs are at the bottom of the forks leg, then unscrew the cap at top fork tube and install the same amount of fork oil as drained out.

Remove forks from bike, with each fork remove end cap and drain plug over a bucket drain oil from each fork reinstall drain plug on lower leg, replace oil thought top of the fork to spec, replace end caps and bleed oil from forks

Instructions

1. • 1 Remove the front tire with the crescent wrench and set aside. Remove the nut and axle bolt from the tier and use the hammer to remove the axle bolt from the forks.
     
   • 2 Remove the securing bolt at the top of the fork on the handle bars. Slide the forks out of the fittings.
     
   • 3 Place the forks into the oil pan, bottom down, and remove the oil nut. Let the forks drain for ten minutes into the oil pan.
     
   • 4 Tighten the oil nuts and remove the seal from the fork fitting with a screwdriver. Slide the seal off the fork.
     
   • 5 Apply oil around the inside of the seal. Slide the seal onto the fork and press into the fitting tightly.
     
   • 6 Replace the oil in the fork following the manufacturer's recommendation.
     
   • 7 Replace the forks and the tire following the steps above in reverse order.
     

Having removed the forks, you will need to undo the lower damper bolt first, this is located on the recess inside the fork where. The spindle goes through, this will then alow you to remove the oil from the fork, and the leg will then be free from the stancion moving freely down, if the fork doesnot come apart, you will have to remove the retaining clip from the seal and pull the fork apart sliding the fork leg up the stancion and sharply pulling down on it to pull the seal out, repeat this till theseal comes out, (tip) undo the fork top nut while the forks are still fitted to the bike.

well first of all,,,,,you dont just top up the fork oil,,,,
you drain it all out and refill it with clean fresh oil....
the reson for this is,,how much oil is left in the forks?
if you over fill them with oil you will burst the top fork sead?? bad news that is! so find the drain plug (a nut or screw) at the bottom of each fork leg and drain all the old oil out first,,, then remove the fork top plug and tip in the right amount of the right grade of oil into each leg,,,then let it stand for a fuw minuets,,for the air to come out,,,do up the fork top plug and push the forks down a fuw times before riding it to spred the oil around inside the forks,,,oh,,by the way,,,change the fork oil yearly,,,,,

lower for legs there should be a drain bolt for each leg do one side at a time.
Take the top fork cap off be careful the top cap is spring loaded get a pan to catch the oil,remove the drain bolt let it drain.reolace the drain bolt then you can add your new fork oil,check your owners manual for the proper amount and weight oil you need to replace, replace the fork cap.
repeat steps on the other fork.

The solutions are close, so I must assume they are HD Road King answers, just not a 1999 Road King. The drain plug is on the front (facing the forks) left side (clutch) of the oil pan. On the 1999 model the drain plug is a 3/4 inch bolt. After changing the oil, be sure to replace the O-ring. The O-ring is rubber and does not last more than a single oil change. HD charges a dollar for the O-ring, but better to replace it than to end up with your new oil all over the garage floor.