On surfaces that are not in contact with people and need to slide, I typically use a 40% MoS2 (moly disulfide) paste. It is pretty expensive but one 4 oz bottle is still nearly full after 20 years. It is black and messy, but it literally bonds to the metal and a thin smear will last an incredible amount of time. I started using it for sear engagements in target triggers set at 1-3 oz let offs. It smooths the motion and makes them more consistent without reducing them. I have since started using it on hinge pins, the nose of cocking hooks and rods etc. In those services it eases friction and gives a smoother motion. A dip on the end of a toothpick will do a trigger sear engagement and last until the next gun cleaning.
I have always been amazed at how much some old guns wear at the joint. I am not sure I could put polishing compound in the joint and have enough energy and time to wear it to the point many seem to reach.
One thing that may play into wear of the system is galling due to similar metals. I don't really know about the metallurgy of Parkers, but I ran into to this when I bought an Ultra Light Arms .22 action several years ago. When I recieved the action, I opened the bolt, examined it and closed it. It was rough and grabbed so much I could hardly remove it again. I greased it with the afore meantioned Moly grease. It worked fine but had to be cycled several times to completely coat and smooth. I called Melvin and was told that you had to be very carefully about maintaining lubrication as the bolt and action weremade of exactly the same alloy and would gall instantly without good lube.
I checked all dimensions and found it to be fit properly and to the same clearances of several modern 22 benchrest actions. Those actions have actions and bolts of greatly different metals and tempers, and don't seem to suffer this trait.
Three things are needed for galling; friction, ductility, and cohesive attraction. These three would all be present in a lot of old doubles. (The attraction occurs most commonly in two similar metals). It may be that the hooks and pins of these older guns are of similar materials and temper, and suffer from more wear than would be anticipated due to the galling effect of the metal itself. The galling typically occurs rapidly in discrete incidents and is not a gradually wearing. I suspect a replacement of a different alloy and temper may last longer with or without grease.
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