georgerkahn,
That's not true at all about the .357 Magnum Marlins. Between my wife and I we have 7 of them, all marked ".357 Magnum". About all they shoot are .38 Special loads, thousands and thousands of them in SASS matches. It's been a year or two since any of them have had a .357 Magnum run through any of them, and we'll be shooting .38 Specials through them again tomorrow morning at our monthly local match.
The key is loading your .38 Special ammunition to at least 1.480" OAL, and using RNFP bullets. You also have to use a firm crimp to keep the bullets from collapsing into the case, which will jam up the gun. They also won't feed wadcutters, period, except single feeding, and who wants a single shot leveraction rifle?
If your gunsmith charged you a lot of money to clear your Marlin, he overcharged you, since all he had to do to clear a feeding jam was remove the magazine cap, barrel ring screw, spring and follower, plus remove the lever screw, lever and bolt. Once that's done, the round will drop out and you just have to put it back together. It takes less than 5 minutes for the whole operation.......
Hope this helps.
Fred