I recently gave up on replacing the mast for the AM/FM radio on my 2000 RX300. Although I can get the replacements rather cheaply on the internet, they would always seem to break when my spouse would sit in the car wash, listening to the radio. (Turning down the volume does not retract the antenna!)
Anyway, with some reading in these forums, I decided to just disconnect the automatic antenna and install something else. However, finding an external mount for the size / angle to replace the automated one, was not easy.
Thus, I spent $5 (free shipping!) for a "concealed" antenna from Ebay. I also went ahead and bought a second one for $5, with an amplifier installed. I would *** AVOID *** the one with the signal booster / amplifier, as it just didn't work and due to signal path, length of power leads, etc. It actually was worse.
This is similar to the one I purchased:
There are lots of them out there, all pretty similar and different prices.
The challenge is removing all the panels and getting to the automatic antenna. I disconnected the automatic antenna, but left it in place so I wouldn't have to try and patch the odd hole.
Hindsight is 20-20: I would take a bit more time to cut the molding just a tad, to accommodate the coax cable. Not a biggie, but mine looks pinched and my "quick fix" cut afterwards looks pretty crappy. If I need to remove the panel in the future, I'll definitely smooth out the area where the coax goes into the molding.
I've included photos so you can see my finished product. It works great. No more broken masts, no more motor noise (because the motor would just run and run when powered on/off) and the signal reception seems quite good.
Additional Hindsight: I would have moved the antenna a bit more centered in the rear window. It works fine where it is, but maybe more centered would be better. Not a big deal.
Hope this helps someone.