There may be a considerable performance discrepancy between simply dousing the shutter in lighter fluid, which will remove soft surface contaminants, and actually cleaning the shutter thoroughly. The latter involves using metal polish on the blades to remove hardened contaminants, which will impede travel due to drag and surface irregularities. For focal plane shutters the problem can be more complex.
All that said, proper testing is absolutely the way to go to determine just how accurate things really are. But having a shutter that doesn't stick is better than having one that does.