If it was me I'd have just cranked the sunroof open from in the trunk and reached in from there....seems simple.  
I just got my hands on a W123 so I am learning all these interesting things about them....
Mine is cranky and doesn't like to start below freezing, took 20 seconds of cranking today at 24F outside. I suspect it needs a major valve adjustment since it has almost 0 blowby when running and is a STRONG engine when driving it. WAY faster than a W126...wow!
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-diesel is not just a fuel, its a way of life- 
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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