Interesting. The first SOLO I bought stayed perfectly snug for about 4 months of steady gigging, then just loosened up a little. That's why I bought a second one, so I could install it and use it while I sent the first one off for the reconditioning service. When it came back, I sent the second one off for recon ... Sort of a cyclical thing you see ...
I attributed the change in fit to either seasonal changes in avg. temperature and humidity, adjustments to my bridge height, or both. Wasn't really sure to be honest.
Is it possible the spruce casing actually compresses (in tiny amounts) somewhat over time from the pressure in the wing slot, thus loosening the fit?
I know Eric dealt with a question like this before in the monster RS thread. But our experiences seem similar Doc.
I never took my first SOLO off the bass for the first several months either. I was so tired of futzing with positioning and fit and shims with my BassMax, I didn't even want to touch the RS because the fit was real snug and the sound was great.