First, NEVER shoot +P ammo in a Colt Agent . . . it can/will stretch the frame and eventually ruin the gun. They weren't designed to handle hot .38 special ammo. Colt doesn't work on these guns anymore, and they have no parts for them either. Worse, rare indeed are competent gunsmiths today who truly understand working on Colt revolvers . . . much less have spare parts to fix 'em!
Second, don't worry about ruining the value of a family heirloom . . . for I doubt you'll ever want to sell it. If you want to make it look nice again, do it. Or . . . leave it the way it is as a conversation piece to tell folks stories about your grandfather!
I have my father's well-worn 1961 Agent. He had a junkyard and carried it for years and years in his backpocket. He never had to shoot anyone with it but it came in handy a few times with rough characters!
My dad wouldn't even put it in a cheap holster and the finish wore pretty bad. Finally, my brother got him a holster and also had the cylinder nickle-plated after a gunsmith buffed off the rust and pitting!
Heck, a chip in the right stock came from when he hit the ground when he died at the junkyard of a massive heart attack at age 81. He never knew he hit the ground!
Ironically, he told me a year or so before he died that he had a weird dream while sleeping one night in his bed that a prowler was in his apartment. He dreamed he'd rolled out of bed and shot at the prowler as the BG was starting to come in his room.
When I got his revolver after he died . . . it had one spent round in the cylinder!!! Checking at his apartment . . . I found a .38 special bullet lodged in the door jamb!
To my knowledge, this is the only time he ever fired it . . . though once, years before, he came across a Highway Patrolman who was getting the crap beaten out of him by a huge bad guy in the middle of nowhere. Dad stopped (of course) and got out. By that time, the trooper was about to lose possession of his own gun!
"Do you need some help?" my lanky dad asked. The trooper replied, "Yes," to which my dad pulled his Colt Agent, pointed it between the BG's eyes and told him to let the trooper go or he'd be one dead ni____r!
The BG understood that the cop HAD to use restraint . . . .but understood that my tough dad wouldn't hesitate to immediately pull the trigger! Dad had a great way of talking to tough folks, and thus this safely ended the threat to the trooper AND the BG . . . who got to go to jail for quite a while! The trooper was VERY grateful too, for dad saving his life. Ahhhh, the stories a gun could tell!
My dad was a part of America's greatest generation . . . and his trusty old Colt was his constant companion. He was a great guy who always did what was right, and I'm so proud to have his Colt Agent.
I'm sure you feel the same way about your grandfather's gun.
Here's dad's, alongside my Model 36 J-frame that is only three years newer (1964). However, that J-frame led a much better cared for life!
PS: All Colt Agent revolvers were "blued," in case you ever decide to get yours refinished. Heck . . . I might just get dad's done one day. Then again . . . his gun has "character!"