I just looked at the old bill from my brake actuator, it lists the part number for the replacement part. 44050-50170

 

Ok, risking my freedom here... Correct replacement part under that internal memo is *****-**4**. That's all I'm going to leak.

 

I think you can go away now lol

 

This is what is published in L-SB-0047-19, December 13, 2019, page 2 of 5 as well. If there is a secret internal document, it's not being released to anyone outside of the dealer network. It wouldn't be a first for Lexus.

 

I'm glad I'm not the only one praying for this.

 

So I actually have a personal interest in this issue. The IS F forum is experiencing increasing numbers of problems with the brake booster as well. The part number for the booster appears to be unique to the IS F, as my parts resource does not show it being used on any other Lexus models including the base model 2IS (200/250/300/350). Does anyone know what the root cause really is? Is there brake fluid leaking from the master cylinder into the booster, or is there mechanical damage, or something else? Most IS F owners discover this problem when going to start the car after sitting overnight. The pedal press is unusually hard because the vacuum has been lost and there is no assist. Initial troubleshooting includes cleaning or replacing the checkvalve - this fixed mine for about 4 years - replacing the checkvalve and the associated hose (this is what I did last time), and now nothing seems to be changing the problem except that it is intermittent. I plan to replace the seal between the master cylinder and the booster next, but I am concerned the issue is brake fluid migration into the booster itself. I've never heard of this before, but apparently this booster issue is more common with the LS than the IS F. Any thoughts or input is appreciated.