Im suspecting my brake fluid is leaking due to the o ring in the master cylinder that most likely needs replacing. What size is this o ring and who sells it?

 

There are no orings per se in the MC.
There are piston seals in the cylinder itself and grommets between the reservoir and cylinder body, but no orings.
I'm sure rebuild kits are available but most folks would just replace the whole unit.

 

Well I mean the o ring that seals the master cylinder between the brake booster. I have the RX-7 repair manual showing the o ring right outside the cylinder. Alright if I have no luck then Ill just buy another unit.

 

If there is an oring between the cylinder and the booster (and there may well be) it's only a dust seal and will not retain fluid.
If the seals are leaking, that oring won't save you.

 

I would just replace the M.C. if I was going to all the trouble to take it off. Depending on were you get it they can be had for less than $50.00. They start at about $23.00 on rock auto.

 

only the S5 t2 has such a thing, as as everyone said if its leaking fluid, the master is bad

 

dont try to bandaid the brake system, replace the master, bleed the entire system

 

Ehh well I guess I might as well just replace it not even costing that much. Thanks everyone

 

It's also recommended to replace the brake booster because when the fluid gets on it, it weakens the diaghram, but you can always wait for a huge vacuum leak. If there was an o ring at the back of the master to brake booster, it is to seal air. Any signs of fluid leaking will be internal seals of the master cyl and you will have a soft brake pedal

You can probably look for a brake mc rebuild kit, but most people just get replacements nowadays