I would suggest getting credit on the cap and replacing it. It shouldn't be necessary to have to re-form a new cap. If the cap has been sitting on the shelf for years and actually needs reformed you don't want that cap.
Replace it with a "NEW" cap.
Cap forming in gereral doesn't work all the time. My experience trying to reform caps is that at best it only buys one a slight amount of time before the cap begins to malfunction again.
The cap boards available now days provide very nice filtering and the ability to replace individual caps as needed at a cost savings. The original cap can be left to provide that original look if needed.