I always think the SP Freak kit is a fair option, the bouns being should you change your marker in the future and it uses a different thread you just spend £20-£30 on a new back.
Paint shouldn't roll out of the barrel though unless it's pea size!! Check that one of your detents has broken, I had one in the past that looked fine but had broken and was just hanging onto itself by a small plastic hinge. Hence it would flap forward and allow the ball to roll out.
Paint shouldn't roll out of the barrel though unless it's pea size!! Check that one of your detents has broken, I had one in the past that looked fine but had broken and was just hanging onto itself by a small plastic hinge. Hence it would flap forward and allow the ball to roll out.