I just saw this discussion today and thought of an earlier post JimLev made about a 1.2 bar cap possibly presenting "a problem with the tu motors running at 108°C on very hot days". Here is the link.
This stuff is a bit beyond me and I did not read through this whole thread, but I thought this info may be useful to some of you who understand better. If this is just cluttering up the thread with unrelated info, let me know and I will delete it.
E39 2003 530i: SP, CWP, PP, Manual, Sunshades, Split folding rear seats, 17" Style 42s
E28 1987 535is: Manual, Bilstein HDs, 16" Style 5v2 (from e38)[Sold]