How would you go about checking for slow leaks? Do you just follow all of the lines that are a part of the brake system and see if anything is loose?

As your brake pads wear, the fluid level in your reservoir will drop. If you are only filling back to the minimum level, it will keep dropping below it as the pads wear. Pull your wheels off and check your pad thickness. Look carefully for any wetness on the calipers or inside the rim, everything should be bone dry. Look at the hoses. It is doubtful that your cap is the culprit. Another possibility is that the master cylinder is leaking inside the brake booster. If you are filling the reservoir to the max line and it is dropping below the minimum line that often, there is a leak somewhere. Best of luck.