Help!! Is this a problem? (Expansion tank replacement)
 

So I'm in the middle of replacing my expansion tank, and I noticed after removing the old tank that a little chunk of plastic has broken off the ridge surrounding the ATF thermostat… Is this going to be a problem and cause a leak? Or do I have to replace that mounting plate also? Also the more I compare pics it looks like maybe the thermostat is also broken? Pics I've seen show them enclosed in black plastic… Also, I noticed after removing that an errant spring had made its way onto the floor. Assuming this was a part of the thermostat? I'm not sure exactly where it came from. Pics attached. Thanks!!!!

Definitely broken - definitely a problem.

BMW E46 Atf thermostat removal and replacement - YouTube

Good thing you caught it!

2002 X5 3.0 264,700 miles
2004 325i 116,500 miles

Thanks for the helpful video link! After viewing, I'm relieved to know that the broken piece is off of the thermostat and not the mounting plate. Didn't want to have to purchase that, too! :D