Breakin seems to be quite important to a ringed engine.

I ran a webra a few months ago, i pushed it a little after only two tanks, and it lost a lot of compression, it is slowly coming back after 20 flights but it doesn't have the compression of a couple OS 50's that i broke in more carefully. the most recent one i decided to treat like the saito folks recomend, ran it sopping rich, never let it get over 160 degrees, (measured with an IR) or over 4000 RPM ran almost a gallon thru it like that and now has fantastic compression.

hard to say if it will fully come back, but it is worth a try, just keep it cool and slow for a few tanks and see what happens.