When you use a vacuum type fluid bleeder and you see some very tiny bubbles going through the tube due to the seal, as long as you have vacuum constantly being applied from the bleeder, air will generally not enter the nipple and into the brake system. Think of it like if you use a straw to drink something, if you keep vacuum (suction) on the straw, it pulls the liquid up; but, if you stop applying vacuum, then it can go back down. I keep constant vacuum (suction) while bleeding, then close the nipple before I stop the vacuum.

 

Redbull, thanks for your explanation. I can't say I did it exactly the way you're describing. I have my fingers crossed. I've been out shopping yesterday and today. The brakes have continued to behave normally. I also took the opportunity to withdraw some fluid from the clutch reservoir and add new brake fluid. This was not a complete flush but a partial renewal. After these procedures, the second O-ring supplied with the kit also expanded and is no longer usable.

 

It depend on the material the o-rings are made from. Some o-rings are more resistant to certain types of chemicals than others.

This website shows the chemical compatibility of various chemicals. You can search under brake fluid, different types of alcohol, etc. of the compatibility of the o-ring type.

https://www.marcorubber.com/o-ring-c...lity-chart.htm

 

Redbull, this hyperlink opens up to a blank page. This seems to be the case for all hyperlinks, they don't work on this forum.

 

Hmm. I'm able to open most hyperlinks.

I tried the link on different browser from different devices (e.g., personal computer, phone, etc.) and it opens up.

This is the webpage address in the image:

 

Redbull, I was able to type in the URL into the browser and open the page. It does provide a lot of detail on how different o-ring materials will interact with different chemicals. Natural rubber is fine but acrylic rubber is not. The catch is I don't know the exact material this o-ring is composed of. It would seem that the bleed kit manufacturer would use appropriate materials for all the parts in the kit. Unfortunately, they have not. All I know is that the o-rings they provided with the kit stretch when in use.

 

I was including that link to look for replacement o-rings that were resistant to brake fluid and alcohol. For replacement o-ring, another sites shows in green, good material for o-rings for brake fluid, ones in yellow are next:

 

Redbull, thank you!