On the subject of hoses, I don't know of a set interval, but my 20 year old TD still has it's original hoses. My first Mercedes was a 1980 300SD. I bought that car when it was 20 yrs old. It to had it's original hoses, which I promptly replaced. When I removed them, the insides were perfect, not a thing wrong with them. Remember, hoses rot from the inside out. I think as long as the hoses don't have soft spots and they look good inside, keep them on.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member