I have the same problem with mid ohio and okyama.
Check out this thread for information about the PLR file. I use it for completely turning off the ghost car, but suspect that you could also adjust the "transparency". There's also a manual off/on toggle in the control settings.
One caveat though: if you turn off the ghost image in the plr and then go online for something like the wtcc pre-qualifying you won't be able to see other drivers on the track. You will be able to hear them though...
http://forum.racedepartment.com/race...ta-replay.html