Ah, that reminds me of another possibility. There are single bulb front corner indicator lenses (with dual filaments), and dual bulb single filament indicator lenses that are available on these cars. The dual bulbs use less wattage than the single bulb by design, if I recall properly.
Someone may have switched out the indicator lenses on your car because they liked the double design over the single design. In that case, I believe there are flasher units that are specifically designed to be used with LED bulbs that have a fixed flash rate regardless of the wattage of the bulbs. I am not sure if it would detect a bulb failure though. I expect that type of flasher relay might solve your problem.
Digging a little deeper, MB302373 is the apparent Mit relay part number for the USA models, and the Wattage is printed on the side.click
The LED compatable relay equivalent appears be here.click
This is all based on my recollection from years ago, and the USA spec parts, so you will have to double check this for yourself. Good luck, hope it helps.