During the entire fishing yesterday, I was feeling something was wrong with one of my 5500CA's. I heard squeaky noise when I cast with it. Today I checked and overhauled it.
I presumed it was due to a damaged ball-bearing, and after I replaced the left one to a new one, I hear the reel make no weird noises any more. Using this opportunity, I checked other inside parts of it, and I found a fact that I didn't notice.
ABU 5500CA is one of the earliest palming-cup type Ambassadeur reels, and some parts are different from those for later palming-cup ones. The left side shims (part #11957, spool centering shim) are o-shaped, and the spool shaft directly meets the bucking space of the left-side cup. After you overuse it, the space become worn and it is irreplaceable.
I guess the ABU thought it bore improvements, and sheet-type shims are used in later reels. Three shims are used in my reel, so I changed the out-most one to a sheet shim. This way, you can replace even if the shim galls.