I hope it is $10 and DONE. Seriously.
I suppose this is a case where gun laws are good for somebody's business.
I don't know the Mk III in detail, but in general, a magazine disconnector has to touch the magazine somehow, so it "knows" when the mag is there, and when it isn't. There are a number of mechanical ways this can be done, and should be done so it doesn't cause any drag on the magazine when ejecting it. But this is seldom the case. To make sure it works, the mechanism is often somewhat overbuilt and does cause drag. On a sport pistol like the Ruger .22, its a small matter, really. On a defensive pistol, its a limitation.
One thing it should never do, on any pistol, is interfere with the magazine seating properly. The kind of problem you have should have been done right at the factory. If it wasn't so complicated and expensive to ship a handgun, it should have gone back to the factory for the fix.
As it is, you're probably better off, and money ahead getting an aftermarket part that will fix your problem (assuming it does). So thank you gun laws (covering shipping) for the jobs you support in the aftermarket industry, and the fact that the maker doesn't have to spend time and money doing warranty support work, which doesn't give them a great deal of incentive to fix the problem or see it is right the first time. Or maybe even know there is a problem....
ohh, are we feeling snarky tonight, or what?
I've got a mark I, had it since the early 80s, and within its limits, its worked so well I never felt any need to "upgrade" to the newer model(s). From what I've heard, Ruger crammed so much poorly thought out cr...er features.. into what was basically a good design that there are a lot of issues with them.
Again, thank you gun laws, and the fear of gun laws yet to come...