Just bought this 06 road king,changed all fluids per manual instructions,but I just read a thread saying to use oil not tranny fluid as the manual says

 

Personally, I would use a gear lube (22oz for your bike) in the tranny. Something like 75/140 or 85/140 such as Mobil 1, Amsoil, Lucas, etc. Many use Redline shockproof heavy. Some do run oil in all 3 holes, but I don't prefer to.

 

I use Gear oil in mine. I tried the Redline syntetic but did not notice a difference so I went back to using Lucas synthetic gear oil cause I can get it locally

 

Just swapped out the Harley blend for the redline,didn't expect it too actually be red! Taking it out later for a ride,old lady dragging me off food shopping