I bought a new master cylinder, from the The Parts Place, it has been on about 2 weeks, every time I drive the car I find a few drips of brake fluid coming from between the booster and the master cylinder. I bought it through there ebay store, I told them through emails that I think the rear seal is bad in it when I put it on, I properly bled the MS and then the whole brake system, TPP asked me what fluid did I use, "Synthetic" I said yes, they said that synthetic is not made for old classic cars, and that it will eat the the rubber seals in the MC and will ruin my calipers! and that I should have used DOT 3 brake fluid and the cap said to only use DOT 3 brake fluid, I replied it is DOT 3 brake fluid but it is synthetic. what do y'all think and what do y'all think I should do? Thanks! Brian

 

Synthetic, is not DOT 3, I think it is DOT 5? And yes, most the old MC say to use DOT3, even if it a new replacement.

 

it says DOT 3 synthetic on the bottle!

 

I think all dot 3, 4 and 5.1 is synthetic now. DOT 5 is silicone. I don't think the Parts Place is correct in their assumption. I also want to hear what others say about this. You should be able to mix/ add Dot 3 with any other 3.

 

I had to buy some DOT 3 today. You are correct, that it says DOT 3 synthetic. It does say, can be used with any DOT 3 fluid. I was wrong about the DOT 5, that is a silicon, not synthetic.