Millmoo

Hi, new member here with only cursory mechanical knowledge. It rained hard last night here in Jersey, and the e39 dash lights lit up this morning- both the yellow D.SC. Light and the red brake light. The pedal felt spongy too. I checked the brake fluid reservoir and that's definitely low, so I assume there must the a leak somewhere. Would it make more sense to take the car to get the rakes checked at a cheap local garage, or should I go to the BMW dealer to get the error codes read first? Btw, there's been Grinding/clunking noise coming from the right front wheel when braking. I assumed it was dust or grit between the pad and disk. Could that be the underlying issue? Thanks, Jezza