2007 RX350 Transmission Question
 

I have a 2007 RX350 with approximately 175k miles. Recently, it's been slipping a bit. I asked my mechanic if a transmission oil change would help. I can't find a record where this has been done, but the transmission oil is not black or burnt smelling.

He said that many times with high mile vehicles, the sand/dirt included in transmission oil helps the transmission to "catch". This helps an older transmission to hang on a bit longer. Changing it could cause the transmission to fail (which it would eventually anyway). Is this the case? Would I be at risk of lessening the life of my transmission (even for a bit) by changing out the transmission fluid? Would changing the filter, gasket and fluid cause this as well or only a complete fluid exchange?

Thanks!

There's a filter you can change inside the pan under drivers side front. Read about it in the DIY sticky. Your clutches could be worn and that is why your mechanic mentioned grit allowing them to catch and change gear, but that's a maybe kind of thing. If you did a filter and fluid swap and it worsened somehow, you could add a friction modifier like what Lucas oil makes or similar. It's your call, but doing nothing certainly won't improve it. Google and research it. Email Lexus and ask them for a recommendation would be a good place to start. After all they built it and have seen it all before.

Very tricky with trannies. Hence we do preventive maintenance with fluid drain and fill. However the new trannies are sealed type and unless you do the mechanical extraction and re-fill, it will be difficult. How did you determine that it was slipping?

Sand/dirt? I might consider finding another mechanic. That said, you need to drop the pan and examine the residue in the bottom of the pan. Finely ground metal and other bits are normal but large pieces indicate excessive wear. If everything looks okay, replace the filter. Reinstall the pan, top up with good quality fluid and test drive.

^^^^This.
My 07 uses WS but has a dipstick so service is easy. Even the so called sealed units have fill and drain plugs so they can and should be serviced with new fluid. Measure the amount you take out, and put that back in. Use the old school method of jumping pins at the OBD2 port or a laser thermometer (Walllyworld has them for 13$) to check when the trans is up to temp then open the fill plug to see if any comes out. If it does, let it drain to a trickle and you're good. If not add fluid and repeat procedure.