Trailer brake issues

[macowneril2015]

I replaced the master cylinder and actuator around 2-3 years ago on my standard trailer. Then last summer and fall I would back it up to the storage facility (only move the boat a few times mainly from storage to harbor and back in the fall) and noticed brake fluid leaking out of the sealed filling port, I had the brakes bleed when I replaced the parts but it was odd to me that it would leak from the master cylinder. I now cannot get the filling top open but was wondering if anyone had any suggestions or ideas? I was maybe thinking brake lines need to be replaced. The trailer does not have that much mileage on it so hopefully its not a full on system replacement.

[Newell]

Open a bleed valve on furtherest wheel, press on actuator if you need to to see if fluid present.

[Jimmyt]

Did you prevent the trailer brake from actuating when backing? Some systems have an electric lock out connected to the backup light circuit in the vehicle. Others have a mechanical pin or tab that you insert when backing to prevent the brakes from actuating. If you haven't locked them out, trying to back up will cause the brakes to actuate.

[Spector]

Drum brakes on that. Something may have locked up in the drum and forced the piston back. I'd pull the wheels and drums and have a look