Cause & Solution to Weeping Green Slime

[Tundratubast]

I have a recurring issue on a Yamaha Bass Bone. Inside the bell at the stem end their is significant weeping of copper green slime that is draining down to the bell flare when left on the the bone stand. I had completed a cleaning and touch up last Thanksgiving 2018. Monday night at rehearsal we took another look and it was worse than before. Now this is the the unlacquered end of the bell. What are my solutions, throughly clean again and attempt to seal the brass with clear coat lacquer??? Thanks.