Is part the issue the silicone seals that keep junque out of the bearings ?? We have tons of linear rails/bearings at work and when the bearing blocks are new sometimes the seals are pretty snug. Do the blocks have grease zerk holes ?? One thing to be aware of (maybe you already know) some blocks if you remove them from the rails ball bearings go everywhere ;-). Trying to find a bind I will loosen all the bolts on all blocks, see if it binds, then snug one block, check, snug the second block, snug the third, check, snug the fourth/last, check. Then if everything is still free start tightening them a little at a time with frequent checks for free motion. Some stuff that was really bound up has freed up just by doing all of that without actually changing anything. We have one system with a pair of rails spaced about 12" apart that run over 8' length..that mess is never happy no matter what you do. About the time we get it working nicely over months somebody decides they see "pitting" which is usually on a non functional part of the rail, and they ask us to replace them :-(.
Bill