If you were planning to keep the rifle (and at that price I would), then a clean without lifting the rib (as per 85lc's suggestion?),
followed by lightly clamping the top-rib in place and soldering (tinning) would be a low-cost first step that may very well end up being the final solution.
I like Brownells Hi-Force 44 btw, which was 95% tin/ 5% silver iirc last time I bought a pound.

But if that doesn't work, I guess you would need to be comfortable with taking it further!