I have a 2006 Volvo D16 VT880. I decided to replace my relay valve and two ABS valves due to a small air leak occurring at the exhaust of the relay valve. This new relay valve is now leaking only when the brake is pressed. It appears that the valve is not closing properly when the brake is depressed and therefore air is passing through the exhaust of the relay valve. This is a different relay valve than my old one, though it is a direct replacement. The new relay valve is a Bendix R-12, if that helps at all.
Please let me know if you have any ideas.