Sorry, I meant to say right front. I have not had my second cup of coffee yet.
I would only replace the one that is bad.
There is a common issue in these transmission that results in a whine and the lurch, which is a harsh shifting. It is a sticking pressure control solenoid.. They tend to stick and cause a high pressure which causes the whining. The repair for this is to replace the solenoid. This is behind the side cover of the transmission. The part is 45 or so, but you do need to remove the transmission part way to get the cover off.
Addatives will not likely do anything to help this.