My 1991 Ford Escort is losing brake fluid but I see no leak. What could it be?

I have had to fill my brake fluid reservoir 2 times in the past 3 months, which is abnormal. What could it be? I see no leak? or:I have had to fill my

I have had to fill my brake fluid reservoir 2 times in the past 3 months, which is abnormal. What could it be? I see no leak?

or:I have had to fill my brake fluid reservoir 2 times in the past 3 months, which is abnormal. What could it be? I see no leak?

Tags:1991,brake,abnormal,