At one time I purchased a MIJ Mosrite Excellent bridge from
Zamm Inc and the string posts/saddles rattled and could be rocked sideways. On the old Mazzrite forum there were several owners of Japanese Mosrites experiencing this problem also. So, I set about to find a remedy. Although this is very elementary, it definitely cured the problem. If the thin white line around the base of the saddle annoy you, I guess the material for the 6-pack Coke handle would work as well. However, once it's assemble and stung up on the guitar it's not noticeable.
As you can see (although not clearly) in the photograph, after disassembly, I glued a paper shim of business card thickness onto the bottom of the saddle post, using cyanoacrylate (Hot Stuff or Super Glue) glue. After the glue set, I then used a pair scissors and trimmed the excess paper around the post. It may be a tight fit to reinstall the intonation screws when putting it back together, but the tighter the better.
