I just dug out my only 114-115 spare VDO clock and opened it up. Unlike the older Mercedes clocks, this one has a one piece
steel case with the chrome bezel crimped over the rim. The 'black ring' on mine is just flat black paint on the inside of the bezel.
Very carefully, with a sharp screwdriver, knife blade, or whatever tool works best for you, it's possible to work loose the crimp on the backside of the bezel. You need to straighten as much as possible the crimp on the backside of the chrome bezel without distortng the front side of the bezel. Then, with whatever sharp tool you prefer, try to gently work the bezel off of the case. Mine has a clear rubber seal under the chrome bezel, then the 'glass', then a cone shaped metal ring and finally, a blue plastic light diffuser behind that ring. There are 3 slotted nuts on the back of the case. 2 of these nuts should already be off after removing the clock from the cluster. remove the third nut and the dial and mechanisim should slide out of the case. When you reassemble it, you will need to figure out how to re-crimp the bezel. Maybe set the clock on a flat surface (with a hole provided to prevent pressure on the dial knob) and roll a round metal bar, ratchet extension, etc against the backside of the bezel.
A final note; My 114-VDO clock is an electric-self winding unit. A discussion on quartz Mercedes clocks that I followed awhile ago indicated that this 'resistor' might be on the circuit board, not inside the clock. I don't have a quartz VDO clock or cluster circuit to dissect.

Happy Motoring, Mark

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DrDKW