New owner! Big problems.....

[Badsmerf]

Hi everyone! I bought a used 2010 x5d with 94k on it. Did not buy from a bmw dealer. Guy knew it had problems, didn't disclose exactly what they were, claimed it had an egr issue. Easy enough i thought. He pledged to help cover costs for fixing it. Turns out it had a bad injector first. Had that replaced, used a used one online to save a bit of money and seller helped with the cost. Great.

It also had thrown the scr inefficient error nox sensor 2. Mechanic told me if the error comes up after the injector is replaced to take it in. After a few days the cel came on, few more days the 200 def fluid incorrect alarm and back to the dealer.

In the meantime, I have been frantically reading forums about these vehicles and learning as much as possible. I also learned from vehicle history the scr cat and both nox sensors were replaced at 80k due to scr failure. Took it to the dealer again (if i keep this truck i need to get software asap). They replace the rear nox sensor and tell me i need a new scr cat now... Wtf? I've never heard of a cat only lasting 15k. I asked how they came to this conclusion since its basically brand new, I was told by service manager the flow was tested and its burnt up. Is it possible the bad injector caused the scr cat to go bad? I'd think the dpf would be more likely since it is first in line?

I know how many emissions related posts there are already. Especially related to nox sensors. I know it's also my first post. Are they throwing parts at it now? How do you determine a bad scr cat? I really want this vehicle to work out, but I can't put a ton of money in it. There are some great minds here, hopefully someone can help.