Hello, I need to top up my master cylinder in 1948 two ton and before I add more fluid (looking for a leak) I want to know if I can use the synthetic dot 3 fluid. I didn't see anything else at the local automotive supply store, and I don't think I could trust asking the young lad behind the counter about the synthetic fluid. Is all brake fluid synthetic now and if the person who owned the truck before me put in non-synthetic can I mix them?
