OK I attempted this today - didn't go as planned. I've backed it out, but I'd like to share some stuff.
First - the part#. RealOEM told me my part# should be 51217202143 so that's what I bought. I found 51217229455 in there. RealOEM has that as an alternate part# although it has been superceded by 51217229461.
I did a whole bunch of searching and I can't find anything specific on 51217202143 vs 51217229455 or 51217229461. Just more people like me asking. The 51217229455 line of parts is harder to get and more expensive, in general.
Looking at parts houses like ECS, FCPEuro etc... they are conflicting in fitment information. Some tell me that 51217202143 won't fit but 51217229461 will. Other say the exact opposite.
I played with the part testing all of the operations - electrical, mechanical - they function identically. They seem to be the same size, shape and weight. If anything, the mounting bolt hole diameter might be slightly larger on 51217202143 but replacement parts do not have threaded holes - they get tapped by the screws. There was enough material for this tapping process to work.
I chickened out and backed it all out, shooting silicone lubricant inside the latch where the connection to the inside lock plunger goes. (On reassembly it is no longer slower than the rest in the car - interesting note).
Other notes on the job. I found broken things and I broke one thing. I think the dealer did a little damage when they were doing a warranty repair.
One point of caution. There are lots of instructions out there about removing the plastic cover behind the interior door handle - making sure to be careful not to insert a tool too far or you will damage fiber optic lighting. It's not just that. The plastic clips on the top right and bottom right (driver's door) are crazy aggressive, and the piece that fails is the DOOR PANEL, not the little plastic cover that you can easily replace. There are youtube videos out there with people saying "it's really tight, it will feel like you will break it - don't worry you won't". YOU WILL.
When doing this on the top you're trying to press a catch about one inch from the right up, reverse on the bottom. Push the little plastic cover opposite while you try to get a tool under there. Every document/video seemed to talk of prying "out" - you need to get in there and release it.
This video @4:00 talks about the problem area. He includes some shots of what you're dealing with. I didn't see this particular one before it was too late. He even says they aren't conducive to ever being removed. He isn't kidding.
https://www.youtube.com/watch?v=omX3GZnVvJc
I worked something out to repair my catches well enough I hope.
Breach's guide is an excellent accompaniment to the other materials out there.