It is easy enough to drain the differential on the 99 RX 300 (from the bottom plug) but I cannot find
the fill hole at the top. Has anyone been able to do so and if so how (without having to become a contortionist) are you able to fill it and check the level? A photo of if would be extremely helpful if possible. Do I need to buy the lexus manual in order to do it?

 

front differential or the rear?

 

Front differential. It is a Front wheel drive model.

 

The plug to the far left is the front differential and the one that is to the right is for the ATF fluid. They both share the same fluid and when you pour in the ATF fluid up top, you are filling both. However, you will also want to drain both.

On my 99 AWD, there is a transfer case nearby that uses 85W90 gear/differential fluid just like the rear differential. Before the end of the month, I plan to change those fluids out (each uses .9 liters) with Royal Purple MaxGear (finally got someone who could import it down here) and will take some pictures.

 

If your car is a front wheel drive, be careful, you may be draining the trani fluid?
Which is no big deal since the front differencial and trani use the same fluid...
You can replenish the same amount of fluid that was removed from the drain holes via the transmission dipstick hole in the engine compartment.

No transfer case fluid to worry about since your FWD

 

Just a thought. Since mine is a Front Wheel Drive and if the two share the same fluids why would there be two seperate drain holes right next to each other?? Why not just drain it all from
the one??

 

From the way I see the diagrams, the differential and the tranny areas where the fluid is are slightly divided by a wall of some sort but not at the top (not exactly sure but then why are there two drain plugs?) I think we mentioned in another thread how some found the fluid that was in the differential to be slightly different looking than the the stuff coming out via the tranny directly, but some also reported no difference.

I am going to be changing mine out again before the end of the month, so I will take pictures of what comes out of both plugs along with the transfer case and rear differential.