Coupler problem on my "new" Lionel 6-18843 RS-3 -- easy to fix?

Looks as if you just need a new coupler assembly; eBay has parts - try searching for couplers for your loco - Lionel made a bunch of these in many road names, if I have the right loco in mind. Installing the coupler is easy.

Also, go to Lionel's website and look at their replacement parts area - check out the RS-3's similar to yours and see if a coupler is available.

I imagine someone here may have parts available, too.

Thanks everybody.  I think I found the part for the complete coupler arm, which looks like it should be easy to replace (remove body and then access screws on top of truck through hole in chassis) and would save me from dealing with the rivet which I don't have tools for.  In case this is useful for someone else, the part number for the coupler arm (which includes the steel thumb tack) is 6108263055 ("coupler/magnetic/plastic/low-end diesel)".

One other concern: the wheels have a rough whitish-silver surface, not the shiny metal I was expecting (but this is the first locomotive I've bought with this kind of wheels).  I don't have a layout to test it on yet so I don't know if this is an issue.  The box looks perfect and there is no rust so I don't think it's been exposed to moisture.  Is this just something that happens over time to the wheels, and if so is it something I need to clean off or will it take care of itself with use?  If this is a serious problem I can still send it back.  Photo below.  Thanks for all the help, hopefully someday I will know something and can help somebody else.
https://drive.google.com/file/...cPv/view?usp=sharing