I have been told that the instrument cluster of an '86 300SDL may be removed from the front of the dashboard by fashioning a hook device, slipping it between the cluster housing and the dash pad, then pull gently. Is this true? My intent is to repair the clock. If there are any known failure modes for the clock, I would appreciate hearing about them. Thanks in advance.

Yes,there has a special tool (hook) to remove instrument cluster.The tool part number is 140-589-02-33-00,You can get it from Mercedes Benz dealer parts dept.(buy a pair) it is very helpfull for DIY job.
About clock repair,Recommend take it to speedo shop.You can fine one in your local Yellow page under auto speedometer section. Good lock

I have repaired a thousand of the clocks with no comebacks!! The information took me a few hours of electronics books to figure out, but here goes. The faiure in the clock circuitry is the two capacitors. They are small round things that look like miniature cans with two pins each and are standing side by side on the board. The trick to getting the clock out is that it is soldered to the chasis after the screws come out. To get it out you will have to locate the little gold colored piece that it is soldered to and de-solder it.
Good luck!!

PS One trade secret down the hatch.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Excellent. Thank you very much for your generosity with your trade secret. You do a great service to the credibility and worthiness of this forum.