My 1989 745T died tonight.
I was crusing about 55 when I started hearing some noise like valve clatter
I saw a little smoke coming from the rear and about that time the engine quit.
I lifted the hood and there was smoke coming from under the intake manifold about where the oil breather is located.
It appears the oil was coming from the dipstick tube; but...
yesterday I removed the oil breather for cleaning and replaced it with a new o ring. It didnt appear to be leaking when I checked it.

I tried to restart the engine with some help, with the oil filler cap off and saw the cam turning normally and all belts were in place.
However the starting noise was different and it wouldnt fire. One cylinder maybe?

One more clue, maybe...
I have been losing oil from the cap and discovered a broken seal which I replaced today. That was the reason for the oil breather cleaning.

I don't know when the timing belt was changed but it was checked recently and passed..

I think the oil issue is separate from the no-start problem but not sure
Any help would be greatly appreciated