wiring harness, power steering leak (this is a chronic issue that requires attention and maintenance constantly. Just manage it and keep an eye on it. pleanty of threads about this issue). keep your coolant fresh and flushed. These cars do not like poor coolant mntc especially in hot climates. They will run very warm otherwise. the '93 may have the retrofit belt tensioner..That's good. the older design is a mntc issue every 60 to 80K. dist caps and rotors every 60 to 80k is good practice. The M119 is rough on those parts. Watch for slow tranny shifts into reverse. Common issue....just watch an plan on correcting it when/if you have the tranny rebuilt at some point (I waited until I had a forward gear shift slip before I put the $$ down for a tranny work over.) at 200K, do a timing chain, guide and rail replacement. (assuming it was not done earlier)
Very few electrical gremlins. a switch here or there...chocked it up to age and mileage.
Very Very solid machine. Tank of a drive train. With regular care and mntc, it will last you a long time. I am in excess of 230K with no signs of stopping

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Jeff
'87 300E
'92 400E
'06 ML350