The key here is to flush the system frequently to prevent there from being a corroded area. Brake fluid(unless you use silicone fluid) has a high alcohol content, and absorbs water out of the air. Keep the reservoir and brake fluid containers sealed.
If you maintain nice, clean fluid in the system, you should have no worries.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in