The opto design flaw was due to inferior semiconductor materials used on the original 1990s components. Electronics have come a long way since those days. The adaptation of RoHS (non Pb content) has forced semiconductor design to accommodate higher temperatures for normal operation.
Current design opto couplers have overcome the reliability issues. Also, one of the biggest problems with the original clock board was the use of four socketed incandescent lamps mounted parallel to the circuit board; they collectively produced excessive heat which damaged the glass epoxy PC board material and copper traces, and prematurely aged the opto couplers, resulting in electrical failure.
That's all been prevented by the use of LEDs. This design uses 12 LEDs to evenly backlight the clock face, with minimal heat being generated. They have been in operation for years now, with near zero defects. The simple design is efficient, without the use of additional components and poses no issues with setting failure codes.