If you change to a
synthetic, make sure you completely,... drain the old fluid out, as they do not mix well.
Since I/we, don't drive our cars regularly, I suck out the master cylinder fluid and add fresh before winter. Water/humidity is the worst enemy in braking systems. I try to use all the fluid from the can because once opened, moisture sets in. If I only use half of it in my cobra, I'll add the rest in my other cars.