scollins - I'd be really curious to know what what your operating coolant temp is. Check out the "hidden menu" discussed above, and you can monitor your coolant temp in real time. If it's in the 73-75 degree range, then I bet you could improve your gas mileage (and maybe preserve your DPF and glow plugs) with a thermostat change. But I do agree with you and ard that one would think the thermostat should last longer (though if it's going to fail, I'm glad it seems to fail open rather than closed).
motordavid - Glad you've been so happy with your e53. I was very happy with mine, hence my subsequently getting the e70. I share some of your frustrations, but overall I think the e70 mechanical experience has been pretty similar to the e53. The e53 that is now driven by one of my sons has roughly 125,000 miles. I had essentially no issues until around 90,000 miles. Then I had what I believe are the usual issues of a "middle aged car" - valve cover gasket, oil filter housing gasket, CCV system (kudos to the Bavauto video on Youtube for that repair), both front control arm bushings, both front CV boots (ditto kudos to the "30 minute CV boot repair" guide on this forum), belt tensioner, idler pulley, and some leaking transmission cooler and power steering hoses. In addition, replaced the thermostat, water pump, and expansion tank as a precaution after hearing about a number of problems from others. With the e70 35d, the only issue I've had (other than the thermostat issue discussed now) has been leaky gaskets on the red charge air hose leading to the intercooler. So I don't think I have too much to complain about for nearly 80,000 miles. Hope I didn't just jinx myself.
ZetaTre - Good to have you chime in, and thanks for all your prior posts. As I stated, some of your posts are what led me to this solution. I saw that you had recommended the transmission thermostat as part of the repair job, but I must confess I just let that sleeping dog lie. I felt that I had enough on my hands as it was. Hope I don't regret it. Great information about the service bulletin on the EGR bracket!! I had no idea, and the work has not been done to my car (since being out of warranty I've done my own maintenance, so it hasn't been in the dealership for awhile). But now I have an appointment for next week to get the bracket put on. Thanks again - you may have saved me from one of the leaking EGR coolers I've read about! I'm a little confused about what you meant by anti-size on high carbon steel flange bolts. What I referred to in my post as "flange bolts" are the part #6 torx bolts in the the diagram below that connect the flange on the semi-flexible hose end of the EGR cooler. These T45 torx bolts are not magnetic. I assume you are talking about the 13 (or 14?) mm hex bolts (part #4) that I referred to as "mounting bolts". Those are magnetic. Anyway, I didn't put any anti-seize on them, but I will when I next do some work in this area!
In addition, I've followed your oil catch can efforts with admiration. Are you happy with your current system, or are you in the midst of another iteration?
Thanks again for the heads up about the mounting bracket service bulletin.