Not obsolete! Marlin did that under advice from lawyers to reduce liabilities for older shotguns. The Model 43 was made into the 1930s of high quality steel, not Damascus. I have one these which I used for years and now my middle son has it. I would avoid magnum steel loads but this is a great SG for upland birds and clays. The patent dates begin in the early 20th century but continue on later.
I used a Model 1897 Winchester Black Diamond SG for goose/duck on the Eastern Shore of Maryland in the early 70s. It was a weaker design than the later hammerless Marlins but digested the #2 magnums without a problem (other than recoil!). I replaced it with a late 30's Steven 520 Ranger and then with a Remington 1100.
I used an 1898 Marlin and later a 97 Winchester (DOM 1910) for Cowboy shooting. SASS outlawed the Marlins after Marlin issued that warning.