I've read and understand the accepted method of 3x3 through the dipstick or upper plug. I'm just wondering what this plug is that is behind the drivers front wheel? It looks and smells like ATF when I remove it.

 

I believe that may be for the differential, the drain plug for the transmission is opposite the oil drain plug under the car.
There is a great post in the DIY forum that's stickied at the top, going over the 3x3 process. Give that a read and it'll go smoothly.

 

RDX trans are rock solid. A 3x3 is great but not totally required on this car. Either way, better to do than not!

Yeah. Diff fluid needs to be changed at some point too. Actually it's a rear diff and front transfer case but I think they need to be changed every 30K miles or so.

 

Don’t know if you can see in the pic, my finger in the background is pointing at the plug that is behind the drivers wheel and the drain plug is in the foreground.

 

Welcome to the forum!

Nice find:

Parts diagram from acurapartswarehouse shows it as a "bolt, plug 20mm" part #90081-PE9-000, *** not all AT case diagrams show it though, no connection to rear differential or the transfer case.

Very interesting there was no ATF spilled when you opened it.
Maybe a factory hole for fill or inspection?

cheers!

 

The next time I change the ATF, I am going to see if the bottom level of that plug corresponds to the dipstick.

 

Thanks let us know