Should i replace brake master cylinder "while i am in there"?

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I need a new brake booster. It caused intermittent problems on cold mornings where first time i would hit the brakes i have hard peddle but no brakes. This only happened a few times. I had a booster go bad about 4 years ago so i know what it feels like. When it went out it was 100% out. I replaced that one with a used one off craigs list. Thats what is in the truck now and giving me intermittent problems. I figure it is time for a new one. I will be going with a City Race new booster.

So here is my question. The brakes in my truck work great. No issues other than what i mentioned. The master cylinder has the new OEM rebuild kit in it that i installed about 3 years ago. I believe it to be good. But i also know that brake booster failures can be caused by masters leaking brake fluid into the booster. I have had 2 boosters fail. One was 190,000 miles and the other was unknown mileage. So it could just be how it goes. Or it could be a bad master. Also, even though my brakes work great. If i start the truck and push the peddle under hard steady pressure it will very slowly sink to a point. I am not loosing any fluid but could the fluid be leaking around the plunger seals in the master to cause a sinking peddle?

I dont think i am loosing fluid but it is a little hard to tell if a small amount is missing. the level will drop as the pads wear. I will top it off maybe once per pads. Then when i put new pads in will remove some fluid so it wont overflow as i compress the pistons.

A new OEM master is "only" $110 from City Racer. I could just order it with the booster and install at the same time for 100% piece of mind. What do you guys think?
 
Doesnt seem like you have a problem. If its wet when you pull it, replace. I wouldn’t buy once just because...
 
I wouldn't fix it if it ain't broke........
 
Usually, if the back of the master is leaking, it will be seeping out between the master and booster, taking the paint off. Changing a good one it's likely to be helpful, but (depending on the year you are working on) the later master is ADVICS BMT-046, ~$70.
 
Are these the same parts? Looking for a master cylinder for a '97.



Or is it the BMT068?

 
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