I've owned an '87 300TD for about a year and a half
now. It's a wagon, but the same basic car nonetheless.

Yes, there are some electrons in the injection system,
but not too many. The Electronic Diesel System (EDS)
controls idle speed, EGR valve, and boost modulation.
The car runs better with the latter two disconnected
It is possible to start and drive the car with the EDS
system failed - I've moved mine while the computer sat
on a shelf in the garage. Idle speed is down near the
'want to stall' level, but that's about the only effect.

Tranny is essentially the same as the 123 cars. Similar
vacuum modulation. Similar set of problems. My experience
is that chasing out any vacuum leaks and tweaking the
Vacuum Control Valve (VCV) fixes things right up.

The trap oxidiser has been fixed forever. They take it
off the car and replace it with an oxidation catalyst
downstream of the turbocharger. On a 124 chassis car,
the entire exhaust system is replaced. I had this done
on my '87 wagon in December 1999. Because it was a
recall, there was no cost, and my local dealer supplied
a loaner car while they performed the work. The car has
better power and better economy following this change out.

I've just recently started using Mobil's Delvac 1 5w-40 in
my diesels. There's no problem running synthetic oil in
this car. In fact, it tends to quiet down the notoriously
noisy hydraulic lifters.

It's a great car, highly recommended. The OM603 engine is
perhaps not quite as bulletproof as the earlier OM617
five cylinder, but has much better power & smoothness with
the same or better economy. These cars sometimes experience
cracked cylinder heads; an expensive repair. I've been
told this failure is associated with overheating resulting
from trapox failure, hence may be moot with the trapox
removed. Don't know, don't care - it's *so* much nicer to
drive than a 123.