I always liked the results from Flitz polish. It brings the brass to a nice shine but doesn't turn colors over time like so many other polishes and it is safe for blueing. Followed up with a wax protection polish by the same company.
There's no telling which pellet will be right. Just takes experimenting until the right one is found.
Resealed? Probably not. Repair service for these models was always spotty. The national service station system didn't come around until 1956 and up till then the only option was to ship the gun back to the factory. By the '60s, service was just about impossible. It's only been with the revival of the vintage Crosmans, and shops like Precision Pellet and MAC-1, that the parts have become widely available again.