It's a vault.
One of the things I most like about my 3 is how solid it is. It is probably the real reason I put up with all the nuisance stuff; to get a vehicle where when you close a door it is just feels solid, is getting more rare each year.
As with most German vehicles, the door hinges are cast metal rather than pressed. The advantage of cast is that it is a bit more rigid than pressed and that helps to make a door opening and closing more precise. That only works is the door posts are not beer can or similar. In other words, a solid piece bolted to a flimsy piece does not work; in the case of the 3, everything is more solid than usual and that is one reason it is so heavy. Actually I think the construction is really unit body mounted on a frame - kind of overkill until it does the 4x4 thing over undulating terrain.
Since we live daily with our 3's we do not even notice the solid way the doors open and close. What I suggest is find a G Wagon somewhere and open and close those doors; they are even more in solid feeling - that was what I was talking about.
Near where I live, there is a level railway crossing -three sets of tracks. I note that I do not slow down for the crossing whereas other vehicles do. For them, it is a combination of weak suspension and lots of body movement; with the 3, it just rolls over the tracks as if they were not there.
As to electrical bits, I have replaced the four wheel height sensors; they wear over the years and give not so accurate readings later in life - not enough to trigger alarms, but just enough to be difficult - a maintenance item. Right after warranty was over, the suspension wiring to the sensors kind of quit/broke/corroded etc and needed repairing/replacement. LR upgraded the wiring on the newer units and the trouble is history.
There is a radio noise capacitor, part number LR020488 located near the tranny. Old age again and when it fails, blows fuse F30E that powers the transmission ECU - engine runs but no go. There is an ignition capacitor under the black plastic cover the again old age; it fails and no spark sometimes. The part number is LR004160 and easy to replace yourself.
Then there is the replacement of the rear upper hatch release switch. Fortunately I can say the replacement switch is an upgrade from the original - that is water cannot get into it any longer - and then there is the brake light switch which it sounds like LR has not upgraded it as the LR4 guys still seem to suffer from it.
The breather cap mod, part number LR019450 is not electrical but is another one of those low cost do it yourself type fix things that can save real money later, same the the tighten the ball screw re the left upper hatch strut.
And then is the the two new sway bar bolts, RYG501580 to replace the existing that where maybe all thread was not the best idea.
O yes, there was the new battery ground cable, YTB500300; seemed OK but I was having what turned out to be starter motor problems and the negative battery cable can have corrosion related concerns.
This stuff is just a nuisance; none of it is a big deal. I could continue the list with the cooling system plastic bits etc, but it all does add up to a continued list of irritants. Anyway, given the the basic drive train is quite strong and the body is solid, my confidence in my 3 continues to improve with time, the reverse of a normal vehicle.