What kind of issues/reliability proboes will i run into on a 103/104?

On my 617 i have rebuilt injectors, done valve adjustments.

What kind of maintenance do you need to do on a 103/104 that isnconsidered 'more taxing to maintain?'

Thanks

It should have the updated wiring harness, updated throttle actuator, updated ovp, updated head gasket. If not you’ll be the one replacing those parts. Not really expensive or hard to replace

Smog pump bearings seem to not last long.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

To add to mr. Speednjay's list are plug wires, cap, rotor, spark plugs and sometimes ignition coil (later m104 have coil-on-plug ignition), m103 timing chains wear out by 140k miles, early 104 motors like to break the EZL and used working ones are worth a lot of money, fuel injectors, if k-jet then the EHA valve can go sometimes, head gaskets don't last 100k on m104 and m103 gasket is a little better but not much. Fan bearing brackets like to go too on both motors.