Who Dunnit? (35d missing bolt after service(s))

[elandfill]

Greetings.. need to pin the rose on who to be mad at..

Long story short, the lower torx bolt on the EGR was loose AND the top EGR bolt on the L bracket was missing (and located under the radiator fan - someone dropped it and just said the heck with it).

2010 BMW X5 35d

Bought the car a year ago.. and have since done the following.. in this order:

1) replaced injector #6 since the bulkhead rain diverter deteriorated and water seeped into the injector. Yes, there's a SIB and extended warranty, but not for diesel (to be discussed in a different thread).
AT BMW Indy Shop in Idaho

2) Takata airbag recall
AT BMW Idaho

3) SCR Tank recall replace
AT BMW IDaho

4) Engine overheating on road trip.. radiator flush, pressurize tank, inspected, replaced expansion cap... did NOT fix problem
AT BMW Indy Shop in Reno

Turns out, overheating was due to corroded thermostat I replaced on the road (at friend's house in SF). To access, we removed EGR (and radiator fan), and noticed the bolt missing up top AND the loose torx at the flange. The top bolt... we located under the radiator fan.. so it was 'dropped' during an earlier repair and the tech. just. left. it. out.

SO.. who in the above 4 repairs would have needed to pull (or loosen) the EGR???
Thus, who may have potentially left the missing bolt, thinking I wouldn't find it

Pretty sure #1 pulled the EGR to release the throttle body and access the plenum up top.. but after that??

thanks!

P.S. YES, I am disappointed the tech in Reno couldn't diagnose a failed thermostat.