1917 DWM Luger Toggle Link Pin problem

[rollin59]

I have a 1917 DWM Luger which I purchased after it had been polished and reblued. Top half is one serial number (all matching) and bottom half is a different serial. Top half and bottom half SN's do not match each other but each assembly is matching. I've fired maybe 200 rounds through it.

Problem recently arose, when firing, the toggle link pin (see photo) slides out partway and blocks the action.
I can slide it back in and continue firing, but the pin keeps popping out of place. There is actually a small nick in the edge of the "lip" on one end of the pin, just visible in photo below.

Others at the range suggested the pin was polished to reblue and is now too small to stay in the hole (this may be true because the 1917 date is barely visible.) The action shouldn't open enough to allow this to happen, but it does.

I do not know any history of the gun other than it came from the Las Vegas Gun Show. I got it from a dealer.

Anything ideas how to correct this problem?