Old SRAM PC-870 chain (top); new SRAM PC-870 chain (bottom).
The chain on my De Rosa started skipping on the lower gears on the Campagnolo 8 speed cassette. Unfortunately, by the time the chain was skipping, the lower cogs on the cassette were worn out.
Measuring from the center of one rivet to the rivet 23 away on a new chain is 12 inches (~30.48 cm). My chain was over 1/4 inch longer. Park Tool recommends replacing the chain when it is 1/16 inch too long.
Replacing the 8 speed cassette is a problem because of the dearth of parts, considering I need a ≥28 tooth lowest cog. I’ve found Miche 13-28 Campagnolo compatible cassettes on eBay in the UK and Italy, but then I start to wonder whether I should keep trying to support shifting components that were last produced in 1997.
I’ve also found on Branford Bike that a Campagnolo 9 speed hub could be used by dropping one sprocket and using a Wheels Manufacturing 8 speed spacer kit, but that spacer kit is also no longer available.
Using the tool is straight forward. One end of the tool threads into the the derailleur mounting hole. Using the tool as a lever allows the hanger to be bent back into alignment. There is an adjustable indicator that measures the run-out from the braking surface of the rim. When that distance is equal at four points (measured at 90 and 270 degrees for horizontal alignment and 0 and 180 degrees for vertical alignment), the derailleur hanger is in alignment.
Park Tool’s video on How to Align a Derailleur Hanger Using the DAG-2.2: