I believe that the only non-lock revolvers S&W is currently making are the Centennial series. They make pretty well all of that series with and without the lock in batches of them.

I have had several 642's since they were first sold in 1991. I cleaned all of them with Hoppes #9 that is probably 15 years old and every now and then, I stripped them completely and rinsed the frames off after the Hoppes scrub with brake parts cleaner. The Hoppes was never on the gun parts for more than a few minutes, the time it took me to scrub each part with a toothbrush. The brake parts cleaner evaporates quickly.

The only finish wear I have experienced has been some wear-through on frame edges, which showed up as black under the wear spots. I never experienced any flaking.

I believe that S&W has changed the finishes on their stainless and aluminum revolvers several times trying to come up with the most durable. the finish they used initially was pretty wear- and solvent-resistant.