The top plate on my Merkur Progress 500 started to need additional pressure during assembly, and then it would pop right off when unscrewing it for disassembly post shave and pre-cleaning.
Looks like I haven't been doing the greatest job drying it after use each time, as the bottom most threads corroded away and became unusable. This caused the need for the additional pressure use the threads that were still intact further up on the screw of the top plate.
This replacement top plate has brought it back to its original functionality and I no longer have to apply excessive pressure during assembly, nor does the plate pop right off the top of the razor during disassembly.