3M makes a product called General Purpose Adhesive Remover that may do the job. But if the glue is really old, it may require taking off some paint to completely get rid of the glue.
The top I removed was the second top the cat wore, so I don't think the glue is too old. I am using a wood chisel to scrape the glue/top backing off, but thought maybe a sander or grinder might be faster and smoother.
Some 40 grit sandpaper makes quick work of it. You need to prime AND paint the roof before installing another top. I recommend a two part primer like PPG brand DP40. Then a topcoat of two part polyurethane.
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