did my first w123 oil cooler lines - just thought I may pass along some tips that other first timers may find helpful.
I used the remove the mount and shock technique after unsuccessful attempts at doing the lines without removing them.

1. remove the shock and the mount - REALLY REALLY makes it a lot easier.

2. I had to jack the motor up till the fan hit the top of the shroud, then remove the shroud clips and jack it up about an inch further - this allowed good access to the top rear 6mm mount bolt.

3. after marring up my engine shock shaft with vice grips to get the bottom bolt off - with it out i noticed a flat spot near the bottom of the shaft that a 7mm wrench fits on to keep it from turning. it is right above where the shaft passes through the body at the bottom.

this was on a 1985.

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1996 E300 110,000
1985 300TD 212,000
1980 300D 238,000