Peter,

I would be undoing the bolts and removing the beams and bolts as a unit, then deal with the problem on a good working surface.

Basically time to sacrifice the bolts and the spacers....plenty of WD40 or similar and then punch them out of the beam.....going to destroy the threads but time to replace them and yes a looser fit works, duralec helps stop the corrosion (dissimilar metal issue) but washing withlots of freshwater helps too....

New bolts and new spacers mate.

DD
"Banh Sidhe"