Balancing is done with a Chadwick or similar machine. If you have simply had the blades off and it was flying OK before its not likely to be balance - plus it has to be quite a bit out to make that much difference.
Most likely, as CD says is an outboard tab bent. The factory may well not have the right settings. I dont think the numerous times mine have been tweaked and blades have been swapped have been reported back to the factory.
If its been knocked out of trim, in my experience it is quicker to start from scratch by zeroing and resetting all the outboard tabs. The procedure for setting the tabs is in the book. Section 12 if I recall right. Dont touch the inboard ones unless you are prepared to get out the chadwick.
Could be a lamiflex gone bad but not that likely.
Unlikely to be air in damper as that usually manifests as big vibrations on cyclic changes. Siezed damper makes it rough all the time. The dampers are easy to check and I'm sure you do it as part of your pre-flight anyway.
I wouldnt bother with the chadwick unless checking flat pitch with reflectors and eliminating cyclic stir with outboard tabs doesnt put things right.
Best of luck.