Why is it cheap? Is that what these cars sell for in Kuwait?

In the US a well documented 600SEL/S600 in the condition you describe is worth around $30,000. Could be a lot more depending on the credibility of the seller. When you see one for half that or less, you have to wonder about the seller's motives. Why is it the most profitable option to give up $20,000 of the car's value? Probably because a) it cost $20,000 to keep it running in the last 12 months, b) there is a $20,000 estimate for 'minor' work that it needs, or both.

To keep one in the US, paying $5-10,000 a year to keep it running should not phase you. I don't know what proportion of these cars actually require that much to keep running but the archives document enough direct experience, not heresay from someone's neighbor's accountant's gardener's nanny's podiatrist, to convince me that it's a likelihood.

I don't know the situation in Kuwait. Maybe there are W140 specialists in every gasoline station since these were popular cars in Kuwait. On the other hand maybe everyone is already drifting from the W220 to the W221 and all the W140 knowledge has been forgotten.

I'm no stranger to MBs with bad reps. I had an 87 300SDL known for developing cylinder head cracks, now have a 93 300SD known for bending rods. I bought both displaying signs of the respective maladies. It's a hobby of mine to get them running properly again. Maybe you're a gambler like me

Sixto
93 300SD