I find myself cursing out the engineers who put older mercs together with annoying regularity. I blame German advanced technology coupled with the need for exacting tolerances in everything. Sometimes I think they deliberately made it difficult on the RHD cars 'cause they lost the war, and all the German vehicles have much easier engines to work on
I think most MB's weren't designed for home or street-corner mechanics, they were meant to go into big shiny dealer workshops with all the right specialist tools and manuals to hand.
Despite usually having an engine bay the size of a house to work with, everything will be crammed together on a merc engine, over-complicated and over-engineered, with the bolt/nut/screw you need to get at buried behind a pipe or other bit of engine accessory, meaning you have to dismantle half the car turning every 5-minute job into an hour + one... I had the thermostat cover off the 250SE the other day- 2 nuts easily accessible and off in seconds, the other 2 buried under the metal fuel delivery lines and so close to the valve cover you can barely get your fingers in and only get a non-ratchet wrench in there and turn a quarter-turn at a time... grrrrr
Saying that, the 124 is actually very easy to work on compared to the 108, with all the filters easy to get to from the top of the engine bay. I think a bit more thought to easy maintenance went into those cars.
Once you've done a job once on the 124, doing it again is (usually) a lot quicker...