Have a Marbles 'buckhorn' style rear sight that is dovetailed into the barrel. Do all Marbles rear sights drift to the right to remove? Thanks.

Been beating the crap out of mine trying to get it to move was the reason I ask. Guess after more than half a century of being in there it isn't anxious to leave. Any suggestions? Thanks.

Soak with Kroll penetrating oil or Break Free. Also possibly heat with heat gun. Would stay away from propane or acetelyne torch.

If it were mine I'd use a warming/ chilling cycle, ( careful use of heat source, I'd probably use an old hair dryer gun and then pour a bit of ice water over it)  followed by a couple sharp raps with a soft face deadblow hammer to the barrel adjacent to the sight to set up some harmonic vibrations should break any oxidation seal. then I'd give it a good Break-Free soak and let it set for a couple days.  Then I'd carefully tap it out with a brass drift.

The heat/chill/vibration/Break-Free system is what my buddies in the old-jeep forums use routinely to handle old rusted bolts and fasteners on our old trucks.  Some of the old captive-nut bed/fender fasteners are unique and nearly irreplaceable and this method has been pretty effective at allowing non-destructive removal.  It should also work on gun parts.