I just bought a 5 screw pre 18. Its been well used barrel and cylinder looks good. But alot of the blue is gone. It is missing the top side plate screw. Serial number 1885XX. If any one could help with a year it was made, and where to get a screw. I would sure appreciate it.
That sounds like 1953 to me. have K196xxx (not shy, just can't remember) that shipped in December of that year.
I think you can get replacement side plate screws from Dave Chicoine (oldwestgunsmith.com) or Poppert's Gun Parts (you can Google his website). Or maybe somebody here has one that they can offer you.
I had the identical situation occur when I found my Pre-18, I called S&W and ordered a replacement, the (Classic)revolvers have the top screw and they fit (OR DID FIT) perfectly!