I have no reservations about opening a freewheel up, the only problem comes when it is stuck and my cheap spanner won't do the job.
I open it up over a 5 gallon bucket to catch everything, clean it all up and use grease to hold the bearings in place. I have never had a problem with it.
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1971 Paramount P-13 Chrome
1973 Paramount P-15 Opaque Blue
1974 Raleigh Professional Blue Mink
1991 Waterford Paramount
Holland Titanium Dura Ace Group
Holland Titanium Ultegra Triple Group