I have an '06 R52 JCW will the 6-speed manual transmission. It's got a slight gear clash when upshifting or downshifting into 4th gear only. The trans fluid is new and full.

I want to try an additive to put into the trans fluid to see if I can get the gear clash to stop or at least try to lessen the noise. I'm not holding my breath on the addition of the friction modifier working, but for $15 for both bottles, right now it's just a gamble before I have to get another transmission or have this one fixed.

My question is this:

I don't want to jack up the car and squeeze the additive into the trans fluid fill hole, is there any other way to add these little bottles of additive to the inside of the trans?

I was wondering if I could remove the backup light switch and get the fluid to the inside of the trans from there

Any other options I could take as well?

Bryan