While I was changing to spark plugs, I noticed a black rubber-ish hose that connects from the top of the intake manifold to the top of the right (passenger side) exhaust manifold was all soft, full of cracks and almost fallen completely apart to pieces. What is this hose for ? The car seems to run fine and normal even with this hose not connected ?

Please help and TIA for any answers.

That would be your crankcase breather / PCV hose.

Definitely replace that hose. With it disconnected, the crankcase is sucking in unfiltered air (that's why it comes from the intake manifold).

Furthermore, when your load is mid to high, the flow of air reverses, pushing blow-by gasses from the crankcase to the intake. So, without it connected, your intake is leaking vacuum, sucking in air from the hot, dusty, engine compartment, bypassing your fresh air ram intake and air filter.

Plenty of online retailers sell it. About $25 bucks, give or take. Part number 1190901982.

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Yeah, mine was disintegratd after 160K miles which I replaced.

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85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

yea mine is getting loose it is original like 4 sections,I see the new ones are one piece less leaks! trying to plug up all the vacum leaks at 259K

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg