I'm afraid I may become a bit of a pest here until I get my feet under me, but what would be the best thing to clean the metal on old Benjamin's seeings as the black finish appears to be fragile? Normal firearm solvents would more than likely be a little harsh I'm thinking...
Hoppe's is generally to be avoided on airguns. It can be tough on rubber or plastic parts, and really is not required as there is no powder or primer residue to deal with of course. My personal favorite all-purpose lube/cleaner is Ballistol. It is mostly medical grade mineral oil, with some solvents added. Fabulous cleaner, but safe to use on any metai, plastic, rubber, or wood surface, and leaves a long-lasting film that is not sticky or gummy. My only choice for bore cleaning and wiping down exterior surfaces. Since you mentioned vintage guns I will mention that's been my thing for 30+ years and I own dozens of 'em. They all love Ballistol.
Just about the only downside of Ballistol is that it stinks!